USRE40056E1 - Methods of controlling communication parameters of wireless systems - Google Patents

Abstract

The present invention provides a method for controlling a communication parameter in a channel through which data is transmitted between a transmit unit with M transmit antennas and a receive unit with N receive antennas by selecting from among proposed mapping schemes an applied mapping scheme according to which the data is converted into symbols and assigned to transmit signals TS_p, p=1 . . . M, which are transmitted from the M transmit antennas. The selection of the mapping scheme is based on a metric; in one embodiment the metric is a minimum Euclidean distance d_min,rxof the symbols when received, in another embodiment the metric is a probability of error P(e) in the symbol when received. The method can be employed in communication systems using multi-antenna transmit and receive units of various types including wireless systems, e.g., cellular communication systems, using multiple access techniques such as TDMA, FDMA, CDMA and OFDMA.

Description

RELATED APPLICATIONS

This patent application is a continuation-in-part of patent application Ser. No. 09/464,372 filed on Dec. 15, 1999, which is herein incorporated by reference.

FIELD OF THE INVENTION

The present invention relates generally to wireless communication systems and methods, and more particularly to controlling a communication parameter between transmit and receive units with multiple antennas.

BACKGROUND OF THE INVENTION

Wireless communication systems serving stationary and mobile wireless subscribers are rapidly gaining popularity. Numerous system layouts and communications protocols have been developed to provide coverage in such wireless communication systems.

The wireless communications channels between the transmit and receive devices are inherently variable and thus their quality fluctuates. Hence, their quality parameters also vary in time. Under good conditions wireless channels exhibit good communication parameters, e.g., large data capacity, high signal quality, high spectral efficiency and throughput. At these times significant amounts of data can be transmitted via the channel reliably. However, as the channel changes in time, the communication parameters also change. Under altered conditions former data rates, coding techniques and data formats may no longer be feasible. For example, when the channel performance is degraded the transmitted data may experience excessive corruption yielding unacceptable communication parameters. For instance, transmitted data can exhibit excessive bit-error rates or packet error rates. The degradation of the channel can be due to a multitude of factors such as general noise in the channel, multi-path fading, loss of line-of-sight path, excessive Co-Channel Interference (CCI) and other factors.

By reducing CCI the carrier-to-interference (C/I) ratio can be improved and the spectral efficiency increased. Specifically, improved C/I ratio yields higher per link bit rates, enables more aggressive frequency re-use structures and increases the coverage of the system.

It is also known in the communication art that transmit units and receive units equipped with antenna arrays, rather than single antennas, can improve receiver performance. Antenna arrays can both reduce multipath fading of the desired signal and suppress interfering signals or CCI. Such arrays can consequently increase both the range and capacity of wireless systems. This is true for wireless cellular telephone and other mobile systems as well as Fixed Wireless Access (FWA) systems.

In mobile systems, a variety of factors cause signal degradation and corruption. These include interference from other cellular users within or near a given cell. Another source of signal degradation is multipath fading, in which the received amplitude and phase of a signal varies over time. The fading rate can reach as much as 200 Hz for a mobile user traveling at 60 mph at PCS frequencies of about 1.9 GHz. In such environments, the problem is to cleanly extract the signal of the user being tracked from the collection of received noise, CCI, and desired is signal portions summed at the antennas of the array.

In FWA systems, e.g., where the receiver remains stationary, signal fading rate is less than in mobile systems. In this case, the channel coherence time or the time during which the channel estimate remains stable is longer since the receiver does not move. Still, over time, channel coherence will be lost in FWA systems as well.

Antenna arrays enable the system designer to increase the total received signal power, which makes the extraction of the desired signal easier. Signal recovery techniques using adaptive antenna arrays are described in detail, e.g., in the handbook of Theodore S. Rappaport, Smart Antennas, Adaptive Arrays, Algorithms, & Wireless Position Location; and Paulraj, A. J et al., “Space-Time Processing for Wireless Communications”, IEEE Signal Processing Magazine, Nov. 1997, pp. 49-83.

Prior art wireless systems have employed adaptive modulation of the transmitted signals with the use of feedback from the receiver as well as adaptive coding and receiver feedback to adapt data transmission to changing channel conditions. However, effective maximization of channel capacity with multiple transmit and receive antennas is not possible only with adaptive modulation and/or coding.

In U.S. Pat. Nos. 5,592,490 to Barratt et al., 5,828,658 to Ottersten et al., and 5,642,353 Roy III, teach about spectrally efficient high capacity wireless communication systems using multiple antennas at the transmitter; here a Base Transceiver Station (BTS) for Space Division Multiple Access (SDMA). In these systems the users or receive units have to be sufficiently separated in space and the BTS uses its transmit antennas to form a beam directed towards each receive unit. The transmitter needs to know the channel state information such as “spatial signatures” prior to transmission in order to form the beams correctly. In this case spatial multiplexing means that data streams are transmitted simultaneously to multiple users who are sufficiently spatially separated.

The disadvantage of the beam-forming method taught by Barratt et al., Ottersten et al., and Roy III is that the users have to be spatially well separated and that their spatial signatures have to be known. Also, the channel information has to be available to the transmit unit ahead of time and the varying channel conditions are not effectively taken into account. Finally, the beams formed transmit only one stream of data to each user and thus do not take full advantage of times when a particular channel may exhibit very good communication parameters and have a higher data capacity for transmitting more data or better signal-to-noise ratio enabling transmission of data formatted with a less robust coding scheme.

U.S. Pat. No. 5,687,194 to Paneth et al. describes a Time Division Multiple Access (TDMA) communication system using multiple antennas for diversity. The proposed system exploits the concept of adaptive transmit power and modulation. The power and modulation levels are selected according to a signal quality indicator fed back to the transmitter.

Addressing the same problems as Paneth et al., U.S. Pat. No. 5,914,946 to Avidor et al. teaches a system with adaptive antenna beams. The beams are adjusted dynamically as the channel changes. Specifically, the beams are adjusted as a function of a received signal indicator in order to maximize signal quality and reduce the system interference.

The prior art also teaches using multiple antennas to improve reception by transmitting the same information, i.e., the same data stream from all antennas. Alternatively, the prior art also teaches that transmission capacity can be increased by transmitting a different data stream from each antenna. These two approaches are commonly referred to as antenna diversity schemes and spatial multiplexing schemes.

Adaptive modulation and/or coding in multiple antenna systems involve mapping of data converted into appropriate symbols to the antennas of the transmit antenna array for transmission. Prior art systems do not teach rules suitable for determining such mappings under varying channel conditions. Specifically, the prior art fails to teach efficient methods and rules for mapping data signals to antennas in systems using multiple transmit antennas and multiple receive antennas in order to control one or more communications parameters under varying channel conditions. Development of methods and rules for selecting appropriate mapping schemes from the many possible choices would represent a significant advance in the art.

SUMMARY

The present invention provides a metric for selecting appropriate mapping schemes for transmitting data while controlling a communication parameter in a channel between a wireless transmit and receive unit, both using multiple antennas. The method of the invention teaches how to select mapping schemes based on the metric which takes into account a quality parameter of received signals or received data.

The method of the invention calls for controlling a communication parameter in a channel through which data is transmitted between a transmit unit with M transmit antennas and a receive unit with N receive antennas. The method calls for providing proposed mapping schemes according to which the data or bit stream is converted into symbols and assigned to transmit signals TS_p, p=1. . . M, which are transmitted from the M transmit antennas. A measurement of the channel at the receiver, e.g., a determination of the channel coefficients matrix H, is used to compute a minimum Euclidean distance d_min,rxof the symbols when received in each of the proposed mapping schemes. This computation can be performed based on H and the proposed mapping schemes only. In this embodiment the minimum Euclidean distance d_min,rxis used as a metric for selecting from the proposed mapping schemes an applied mapping scheme to be employed for transmission of the data. The selection of the mapping scheme based on the minimum Euclidean distance metric d_min,rxallows one to control the communication parameter.

The data can be converted into symbols in accordance with any suitable modulation technique. For example, the data can be converted into symbols modulated in constellations selected from among PSK, QAM, GMSK, FSK, PAM, PPM, CAP, CPM or any other modulation scheme associating data with a constellation. The mapping scheme can involve coding the data at certain coding rates. Furthermore, the mapping scheme can include at least one method selected from among diversity coding and spatial multiplexing.

When the mapping scheme includes diversity coding a k-th order diversity coding, where k ranges from 1 to M, can be used. The diversity coding can be selected from techniques consisting of space-time block coding, transmit antenna selection, Equal Gain Combining (EGC), Maximum Ratio Combining (MRC) and delay diversity coding or any other antenna diversity scheme. Alternatively, the diversity coding can include a random assignment of the transmit signals TS_pto k of the M transmit antennas. In accordance with yet another approach, the assignment of the transmit signals TS_pto k of the M transmit antennas can be based on a required minimum Euclidean distance d_min,required. The required minimum Euclidean distance can be determined based on its relation to one or more quality parameters that the transmitted data has to maintain. For example, the quality parameter can be signal-to-interference noise ratio, signal-to-noise ratio, power level, level crossing rate, level crossing duration, bit error rate, symbol error rate, packet error rate, and error probability.

When the mapping scheme includes spatial multiplexing a k-th order spatial multiplexing (where k ranges from 1 to M) can be used. Spatial multiplexing can involve random assignment of the transmit signals TS_pto k of the M transmit antennas. Alternatively, the assignment of the transmit signals TS_pto k of the M transmit antennas can be based on the required minimum Euclidean distance d_min,requirednecessary to maintain one or more of the quality parameters.

It is convenient to store a minimum Euclidean distance d_min,trof the symbols when transmitted in a database. The database can reside in the transmit unit or in the receive unit (or it can be available in both).

Among others, the communication parameter to be controlled can include data capacity, signal quality, spectral efficiency or throughput.

It is advantageous to establish a relation between the quality parameters and the required minimum Euclidean distances d_min,requirednecessary to satisfy the quality parameters, i.e., maintain the quality parameter above a specified threshold. The relations between the minimum Euclidean distances d_min,requiredfor all possible mapping schemes and the corresponding quality parameters are also conveniently stored in a database.

The method of the invention can be employed in communication systems such as wireless systems, e.g., cellular communication systems, using multiple access techniques selected from among TDMA, FDMA, CDMA and OFDMA. In conjunction with these techniques the mapping schemes can include diversity coding selected from techniques including space-time block coding, transmit antenna selection, Equal Gain Combining (EGC), Maximum Ratio Combining (MRC) and delay diversity coding or any other antenna diversity scheme.

In another embodiment of the invention the metric used is the probability of error, P(e). In this case the measurement of the channel is used to compute for each of the proposed mapping schemes a probability of error P(e) in the symbol when received. The applied mapping scheme is then selected from the proposed mapping schemes based on the probability of error P(e) to control the communication parameter.

The proposed mapping schemes in this embodiment can include random or determined assignment of transmit signals TS_pto k of the M transmit antennas as discussed above both in case of diversity coding and spatial multiplexing. In particular, the assignment can be based on a required probability of error P(e)_req.

The invention further encompasses a communication system which uses the minimum Euclidean distance d_min,rxof said symbols when received, to select the applied mapping scheme from among the proposed mapping schemes. The invention also includes a communication system which uses the probability of error to select the appropriate applied mapping scheme.

A detailed description of the invention and the preferred and alternative embodiments is presented below in reference to the attached drawing figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a simplified diagram illustrating a communication system in which the method of the invention is applied.

FIG. 2 is a simplified block diagram illustrating the transmit and receive units according to the invention.

FIG. 3 is a block diagram of an exemplary transmit unit in accordance with the invention.

FIG. 4 is a block diagram of an exemplary receive unit in accordance with the invention.

FIG. 5A is a detailed block diagram illustrating a selection block and related components involved in selecting an applied mapping scheme from proposed mapping schemes based on a minimum Euclidean distance metric.

FIG. 5B is a detailed block diagram illustrating a selection block and related components involved in selecting an applied mapping scheme from proposed mapping schemes based on a probability of error metric.

FIG. 6 is a block diagram of another transmit unit in accordance with the invention.

DETAILED DESCRIPTION

The method and wireless systems of the invention will be best understood after first considering the high-level diagrams ofFIGS. 1 and 2.FIG. 1 illustrates a portion of awireless communication system10, e.g., a cellular wireless system. For explanation purposes, the downlink communication will be considered where a transmitunit12 is a Base Transceiver Station (BTS) and a receiveunit14 is a mobile or stationary wireless user device. Exemplary user devices include mobile receiveunits14A,14B,14C which are portable telephones and car phones and a stationary receiveunit14D, which can be a wireless modem unit used at a residence or any other fixed wireless unit. Of course, the same method can be used in uplink communication fromwireless units14 toBTS12.

BTS12 has anantenna array16 consisting of a number of transmitantennas18A,18B, . . . ,18M. Receiveunits14 are equipped withantenna arrays20 of N receive antennas (for details seeFIGS. 2,3 and4).BTS12 sends transmit signals TS to all receiveunits14 viachannels22A and22B. For simplicity, onlychannels22A,22B betweenBTS12 and receiveunits14A,14B are indicated, althoughBTS12 transmits TS signals to all units shown. In this particular case receiveunits14A,14B are both located within onecell24. However, under suitable channel conditions BTS12 can transmit TS signals to units outsidecell24, as is known in the art.

The time variation ofchannels22A,22B causes transmitted signals TS to experience fluctuating levels of attenuation, interference, multi-path fading and other deleterious effects. Therefore, communication parameters ofchannels22A,22B such as data capacity, signal quality, spectral efficiency or throughput undergo temporal changes. Thus,channels22A,22B can not at all times support efficient propagation of high data rate signals TS or signals which are not formatted with a robust coding algorithm.

In accordance with the invention,antenna array16 atBTS12 can be used for spatial multiplexing, transmit diversity or a combination of the two to reduce interference, increase array gain and achieve other advantageous effects.Antenna arrays20 at receiveunits14 can be used for spatial multiplexing, receive diversity or a combination of the two. All of these methods improve the capacity, signal quality, range and coverage ofchannels22A,22B. The method of the invention finds an optimum choice or combination of these techniques chosen adaptively with changing conditions ofchannels22A,22B. The method of the invention implements an adaptive and optimal selection of spatial multiplexing, diversity as well as rate of coding and bit-loading over transmitantenna array16 toantenna array20.

Specifically, the method of the invention addresses these varying channel conditions by adaptively controlling one or more communication parameters based on a metric.FIG. 2 illustrates the fundamental blocks of transmitunit12 and one receiveunit14 necessary to employ the method. Transmitunit12 has acontrol unit26 connected to adata processing block28 for receivingdata30 to be converted and mapped in the form of transmit signals TS in accordance with a number of proposed mapping schemes to transmitantennas18A,18B, . . . ,18M for transmission therefrom. An up-conversion andRF amplification block32 supplies the transmit signals TS toantennas18A,18B, . . . ,18M.

On the other side of the link, receivingunit14 has N receiveantennas34A,34B, . . . ,34N in itsarray20 for receiving receive signals RS. An RF amplification and down-conversion block36 processes receive signals RS and passes them todata processing block38.Data processing block38 includes a channel measurement or estimation unit (seeFIG. 4) which obtains a measurement of the channel coefficients matrixH characterizing channel22.

A metric-basedprocessing unit40 uses matrix H and knowledge of the proposed mapping schemes to select an applied mapping scheme which should be used by transmitunit12. In particular, given a communication parameter which is to be controlled, e.g., maximized or kept within a prescribed range,unit40 makes a decision about which of the proposed mapping schemes should be selected as the applied mapping scheme under prevailing conditions ofchannel22. This selection is fed back as indicated by dashedline42 to transmitunit12. Incase channel22 is a time-division duplexed (TDD) channel, which is reciprocal between the receive and transmit units, no separate feedback is required. In response,unit26 employs the applied mapping scheme in processingdata30. This ensures that a selected communication parameter or parameters are controlled.

An exemplary embodiment of a transmitunit50 for practicing the method of the invention is shown in FIG.3.Data52, in this case in the form of a binary stream, has to be transmitted. Before transmission,data52 may be interleaved and pre-coded by interleaver and pre-coder54 indicated in dashed lines. The purpose of interleaving and pre-coding is to render the data more robust against errors. Both of these techniques are well-known in the art.

Data52 is delivered to a conversion unit, more specifically a coding andmodulation block56.Block56converts data52 into symbols at a chosen modulation rate and coding rate. For example,data52 can be converted into symbols through modulation in a constellation selected from among PSK, QAM, GMSK, FSK, PAM, PPM, CAP, CPM or other suitable constellations. In this embodiment,data52 is modulated in accordance with 4QAM, represented by aconstellation58 with four points (the axes Q and I stand for quadrature and in-phase). In particular,data52 is 4QAM modulated at a certain modulation rate and coding rate. The transmission rate or throughput ofdata52 will vary depending on the modulation and coding rates.

Table 1, below, illustrates some typical modulation and coding rates with the corresponding constellations which can be used in the proposed mapping schemes. The entries are conveniently indexed by a mapping index.

TABLE 1
	Modulation				Output
Mapping	Rate	Coding	Throughput		Constel-
Index	(bits/symbol)	Rate	(bits/s/Hz)	dmin,tx	lation

1

1

1

1

4

BPSK

2	1	½TCM	1	7.2	4	PAM
3	2	1	2	2	4	QAM
4	2	⅔TCM	2	4.3	8	PSK
5	3	1	3	0.58	8	PSK
6	3	¾TCM	3	1.32	16	PSK
7	4	1	4	0.4	16	QAM
8	4	⅘TCM	4	0.8	32	QAM

In this table minimum Euclidean distances d_min,txare listed with symbol energies E_snormalized to equal 1. The abbreviation TCM stands for Trellis Coded Modulation, which is well-known in the art and involves the simultaneous application of coding and modulation. The mapping index column can be used to more conveniently identify the proposed constellations, modulation and coding rates which are to be used as part of the proposed mapping schemes.

Tables analogous to Table 1 for other constellations can be easily derived. Specifically, similar tables can be produced for constellations GMSK, PPM, CAP, CPM and others. It should be noted that modulation and coding are well-known in the art.

The next to last column of Table 1 indicates a minimum Euclidean distance d_min,txin the constellation, where the subscript tx indicates the transmit side. This is the shortest distance between any two points in the constellation. The minimum Euclidean distance between two points in4QAM constellation58 is indicated by a solid line. A longer distance dt, is also indicated in a dashed line. The code used increases this minimum Euclidean distance d_min,txas is clear from in Table 1. The minimum Euclidean distances for any other can be calculated or obtained from standard tables. For more information on the derivation of these distances see Stephen B. Wicker, Error Control Systems for Digital Communication and Storage, Prentice Hall, 1995,Chapter 14.

Once coded and modulated in symbols,data52 passes to aswitch60. Depending on its setting, switch60routs data52 either to aspatial multiplexing block62 or to adiversity coding block64. Both blocks62 and64 have a number k of outputs, where k≦, to permit order k spatial multiplexing or order k diversity coding. A switchingunit68 is connected toblocks62 and64 for switching the k order spatially multiplexed or k order diversity coded signals to its M outputs. The M outputs lead to the corresponding M transmitantennas72 via an up-conversion andRF amplification stage70 having individual digital-to-analog converters and up-conversion/RF amplification blocks74.

Together, switch60, blocks62,64 and switchingunit68 act as an assigningunit76 for assigningdata52 to transmit signals TS_p, where p=1. . . M, for transmission from the M transmitantennas72. It should be noted that for spatial multiplexing of order k or diversity coding of order k, where k<M, not allantennas72 may be assigned transmit signals TS_p. The criteria for selecting which ofantennas72 will be transmitting transmit signals TS_pwill be discussed below.

Thus,data52 undergoes conversion into symbols and assignment to transmit signals TS_pwhich are transmitted fromantennas72. This conversion and assignment ofdata52 represent a mapping scheme. Specifically, all the possible combinations of conversions and assignments represents possible or proposed mapping schemes which can be used bytransmitter50 to transmitdata52 from itsM antennas72 overchannel22.

Transmitunit50 also has acontroller66 connected to coding andmodulation unit56 and to switch60. Adatabase78 of proposed mapping schemes is connected tocontroller66.Database78 conveniently contains tables, e.g., two tables: one for diversity coding and one for spatial multiplexing, or one integrated table or look-up table for both diversity coding and spatial multiplexing. The table or tables contain modulation rates, coding rates, throughputs, and minimum Euclidean distances for mapping schemes employing diversity coding and for mapping schemes employing spatial multiplexing. The tables or table can also include a mapping index column, as does table 1, to simplify the identification of the coding and modulation rates to be used in the proposed mapping schemes. In an integrated table the mapping index can serve as a mapping scheme index to identify all mapping parameters, i.e., whether diversity coding or spatial multiplexing is employed and at what coding rate, modulation rate, throughput and associated minimum Euclidean distance. The convenience of using one mapping scheme index resides in the fact that feed back of mapping scheme index to transmitunit50 does not require much bandwidth.

Specifically, transmitunit50 receives feedback denoted Rx from receive unit90 (seeFIG. 4) via afeedback extractor80.Feedback extractor80 detects the mapping scheme index and forwards it tocontroller66.Controller66 looks up the corresponding mapping scheme which is to be applied indatabase78. In cases where channel parameters, e.g., channel coefficients matrix H, have to be known to employ the applied mapping scheme (e.g., when the diversity coding technique is Maximum Ratio Combining), receiveunit90 may also send the channel parameters tofeedback extractor80.Extractor80 delivers the channel parameters tocontroller66 as well asdiversity coding block64 andspatial multiplexing block62. In the event of using a time-division duplexed (TDD)channel22, the feedback information, i.e., the channel parameters are obtained during the reverse transmission from the receive unit or remote subscriber unit, as is known in the art, and nodedicated feedback extractor80 is required.

FIG. 4 illustrates receiveunit90 for receiving receive signals RS from transmitunit50 throughchannel22 with N receiveantennas92. Receiveunit90 has an RF amplification and down-conversion stage94 having individual RF amplification/down-conversion/ and analog-to-digital converter blocks96 associated with each of the N receiveantennas72. The N outputs ofstage94 are connected to ablock98 which performs receive processing, signal detection and decoding functions. The N outputs ofstage94 are also connected to achannel estimator100.Channel estimator100 obtains a measurement ofchannel22; in particular, it determines the channel coefficients matrix H representing the action ofchannel22 on transmit signals TS_p.

Estimator100 is connected to block98 to provideblock98 with matrix H for recovery ofdata52. Specifically, block98 uses matrix H to process the received signals RS prior to reversing the operations performed ondata52 at transmitunit50. The output ofblock98 yields the reconstructed data stream. A deinterleaver anddecoder unit102 is placed in the data stream if a corresponding interleaver andcoder54 was employed intransmitter50 to recoveroriginal data52.

Channel estimator100 is also connected to a channelparameters computation block104.Block104 computes the prevailing parameters ofchannel22. In particular, block104 can compute channel parameters such as SINR, Frobenius norms, singular values, condition of channel coefficients matrix H and other channel parameters. The actual computational circuits for computing these parameters are known to a person skilled in the art.

Block104 is further connected to aselection block106.Block106 analyzes receivedconstellation108 which corresponds to transmittedconstellation58 after being subjected to the action of thechannel22, i.e., after channel coefficients matrix H is applied.Block106 selects from the proposed mapping schemes an applied mapping scheme which is to be used inmapping data52 to transmitantennas72 of transmitunit50.

In another embodiment, minimum Euclidean distance d_min,rxcomputed for symbols received is used as the metric for controlling the communication parameter.FIG. 5A illustrates a detailed block diagram showingselection block106 and related components involved in selecting the applied mapping scheme based on minimum Euclidean distance d_min,rx.Block106 contains adatabase108 of the minimum Euclidean distances d²_min,tx; here these are the distance values squared, for allconstellations58 in the proposed mapping schemes on the transmit side. The distance information indatabase108 is associated with the respective proposed mapping schemes and can be ordered in tables for diversity coding and spatial multiplexing with the associated constellations, modulation rates and coding rates in a similar form as indatabase78 discussed above. In fact, likedatabase78,database108 may contain a copy of an integrated table or look-up table as discussed above. For mathematical reasons, it is convenient to work with the square values of the minimum Euclidean distances and the embodiments described herein shall take advantage of this fact.

Database108 is connected to acomputing block110.Computing block110 computes a minimum Euclidean distance d_min,rxfor received symbols based on matrix H ofchannel22. Due to the action ofchannel22 minimum Euclidean distance d²_min,txfor the symbols transmitted from transmitunit50 will have changed in the received symbols. In other words, d²_min,tx≠d²_min,rxbecause of the action of channel coefficients matrix H. The actual change in the minimum Euclidean distance between the transmitted and received constellations will depend not only on the constellation, modulation rate and coding rate but also on the assignment ofdata52 to transmit signals TS_pfor transmission from transmitantennas72. In other words, the minimum distance depends on the entire proposed mapping scheme. Therefore,computing block110 has a sub-block112 for computing d²_{min,Diversity}for received symbols which are diversity coded andsub-block114 for computing d²_min,SMfor received signals which are spatially multiplexed. Both sub-blocks112,114 obtain the value of d²_min,sxfromdatabase108.

The diversity coding methods can include techniques such as space-time block coding, transmit antenna selection, Equal Gain Combining, Maximum Ratio Combining and delay diversity coding. All of these coding methods are described in the prior art. Alternatively, a random assignment of transmit signals TS_pto k of transmitantennas72 can be made. This is especially useful when transmitunit50 is initially turned on, since no stable information aboutchannel22 may be available at that time. The order of the diversity coding methods is k, where 2≦k≦M. Let us designate the throughput at order k=M diversity coding to be r bits/s/Hz. When k<M—fewer than all M transmitantennas72 are being used for diversity—the throughput remains at r bits/s/Hz.Sub-block112 uses the channel coefficients matrix H and d²_min,txfromdatabase108 to compute d²_{min,Diversity}to evaluate diversity coding methods listed above. The mathematics involved in these computations will be addressed below.Sub-block112 then selects from among the d²_{min,Diversity}values the largest one for each data rate r. This is the best selection since it ensures the lowest probability of data corruption or error.

Spatial multiplexing methods are known in the art. Spatial multiplexing in the present invention can involve a prescribed or a random assignment of transmit signals TS_pto k of transmitantennas72. Random transmit antenna assignment is especially useful when transmitunit50 is initially turned on, since no stable information aboutchannel22 may be available at that time. The order of spatial multiplexing is k, where 2≦k≦M. Let us designate the throughput perantenna72 at k-th order spatial multiplexing to be r/k bits/s/Hz. When k<M then M−k transmitantennas72 are used for diversity.

Sub-block114 uses the channel coefficients matrix H and d²_min,txfromdatabase108 to compute d²_min,Smfor the spatial multiplexing methods. The mathematics involved in these computations will be addressed below.Sub-block114 then selects from among the d²_min,SMvalues the largest one for each data rate r. This is the best selection since it ensures the lowest probability of data corruption or error.

Computing block110 is in communication with adecision making circuit116. Both sub-blocks112,114 deliver their choices of the largest d²_{min,Diversity and d}²_min,SMfor each data rate r respectively todecision making circuit116.

In accordance with another embodiment and as indicated inFIG. 5A,decision making block116 is also connected to ablock122 whose function is to determine a required minimum Euclidean distance d²_min,required.Block122 is in communication with communicationparameters computation block104 and with a dataquality parameter block124.

Block124 informs block122 of a quality parameter, e.g., acceptable bit error rate (BER) or other threshold, which has to be observed. In fact, the quality parameter can be any of the following: signal-to-interference noise ratio, signal-to-noise ratio, power level, level crossing rate, level crossing duration, bit error rate, symbol error rate, packet error rate, and error probability. The quality parameter selected can be dictated by the type of service, e.g., fixed rate service, between transmitunit50 and receiveunit90, or by other requirements placed ondata52 or any other aspect of the communication link. As an example, a fixed BER is chosen as the quality parameter in this embodiment. The BER is translated into a corresponding probability of error P(e) and supplied to block122; here P(e) is specifically the probability of symbol error.

Block104 provides block122 with the channel parameters, e.g., channel coefficients matrix H. The channel parameters are included in the derivation of d²_min,required. In the present embodiment, d²_min,requiredis derived directly from the required P(e) using an established relationship:$P\left(e\right)\le N_{e}Q\left(\sqrt{\frac{E_s{d}_{\min ,\mathrm{required}}^2}{2N_o}}\right)$
where N_eis the number of nearest neighbors in the constellation and can be found for each proposed mapping scheme based on the channel coefficients matrix H, Q(x)=½erfc(x/√{square root over (2)}), where erfc is the complementary error function, E_sis the symbol energy and N_ois the noise variance.

When other quality parameters are used, d²_min,requiredcan be derived from other relationships involving different parameters from among those delivered fromblock124 and fromblock104. In any event, the relation between the quality parameter and d²_min,requirednecessary to satisfy the quality parameter should be established.

The value of d²_min,requiredis supplied todecision making circuit116 and the choice between d²_{min,Diversity}and d²_min,SMis made such that the value which exceeds d²_min,requiredand which supports the maximum data rate r is selected. For example, when both values comply with data rate r and are larger than d²_min,requiredthen the larger of the two is chosen. If neither d²_{min,Diversity}or d²_min,SMis satisfactory, then additional proposed mapping schemes are evaluated bysub-blocks112,114 until either one produces a value of d²_minwhich exceeds d²_min,requiredand then this value is chosen.

It should also be noted, that when either diversity coding or spatial multiplexing is employed in the proposed mapping schemes, the assignment of transmit signals TS_pto k of theM antennas72 can be made based on d²_min,required. This assignment can be made by choosing the subset k of M transmitantennas72 which provides the maximum data rate r for the given d²_min,required.

During operation receiveunit90 repeats the computation of d_minaschannel22 changes. In the case of a movingreceiver90, e.g., a cellular telephone, this recalculation should be performed more frequently, since the channel coherence time is short. In case of astationary receiver90, e.g., a wireless modem, the coherence time is longer and d_mincan be recomputed at longer intervals.

This selection is delivered to afeedback118, which passes the choice on to atransmitter120 of the receiveunit90.Transmitter120 sends the choice of the applied mapping scheme characterized by the largest d²_minat the desired data rate r back to transmitunit50. Conveniently,transmitter120 can send the mapping scheme index identifying enabling transmitunit50 to locate and retrieve the applied mapping scheme fromdatabase78.

The applied mapping scheme includes the modulation rate and coding rate, as well as a choice of the diversity method or spatial multiplexing method which yielded that largest d²_minvalue picked atdecision making block116. Advantageously,feedback118 is also connected to channelparameters computation block104, as shown, to additionally transmit back to transmitunit50 the parameters ofchannel22, e.g., the channel coefficients matrix H, determined atreceiver90.

FIG. 5B illustrates an alternative embodiment of the invention in which aselection block150 relies on the probability or error P(e) as a metric to select the applied mapping scheme from the proposed mapping schemes. Analogous blocks in this embodiment retain the reference numbers from FIG.5A. In particular acomputing block152 has twosub-blocks154,156 for computing the probability of error for diversity coding P(e)_Diversityand probability of error for spatial multiplexing P(e)_SMfor each data rate r.

Sub-blocks154,156 are connected to adecision making circuit158. Of the P(e)_Diversityand P(e)_SMvaluescircuit158 chooses the one which is the lowest from the proposed mapping schemes and supports the highest data rate r. This choice is fed back viatransmitter120 to transmitunit50 as in the above-described embodiment.

Preferably, ablock160 provides the d²_min,requiredvalue based on a quality parameter, e.g., a desired BER in the case of fixed BER service, to ablock162 for computing the required probability of error P(e)_required. Once again, the relationship:$P\left(e\right)\le N_{e}Q\left(\sqrt{\frac{E_s{d}_{\min ,\mathrm{required}}^2}{2N_o}}\right)$
can be used in this computation.Block162 used d²_min,requiredas well as channel parameters from communicationparameters computation block104 to compute P(e)required. This computed value of P(e)_requiredis then supplied todecision making circuit158 to select the suitable value from among the P(e)_Diversityand P(e)_SMvalues for the proposed mapping schemes. In this case the lowest value of P(e) is selected.

It should be noted that in the event transmitunit50 receives feedback of channel information, whether using TDD or simple feedback, it could make the selection of applied mapping scheme on its own. In other words, transmitunit50 can select the mapping scheme index and apply the corresponding mapping scheme fromdatabase78. This alternative approach would be convenient when receiveunit90 does not have sufficient resources or power to evaluate the proposed mapping schemes. Of course, transmitunit50 would then contain all the corresponding computation and decision-making blocks contained in receiveunit90 as described above.

FIG. 6 illustrates another embodiment of a transmitunit200. Corresponding parts have been labeled with the same reference numbers as in FIG.3. In this case,data52 to be transmitted is first delivered to aswitch202. Depending on the setting ofswitch202data52 is passed either to a coding andmodulation block204 andspatial multiplexing block206 or to a space-time coding block208. In this embodiment space-time coding block208 assumes all the functions of coding, modulating and applying a diversity technique todata52. Meanwhile, blocks204 and206 implement coding, modulation and spatial multiplexing respectively.

Bothblocks206 and208 have a number k of outputs, where k≦M, to permit order k spatial multiplexing or order k diversity coding respectively.Switching unit68 is connected toblocks206 and208 for switching the k order spatially multiplexed or k order diversity coded signals to its M outputs. The M outputs lead to the corresponding M transmitantennas72 via up-conversion andRF amplification stage70 having individual digital-to-analog converters and up-conversion/RF amplification blocks74.

Together,switch202, blocks204,206,208 and switchingunit68 act as an assigningunit210 for assigningdata52 to transmit signals TS_p, where p=1. . . M, for transmission from the M transmitantennas72. As in transmitunit50, the criteria for selecting the applied mapping scheme will dictate the setting ofswitch202 and operation ofblocks206,208,68. In other words, the applied mapping scheme will be used to set all parameters of assigningunit210. As before, this function is achieved with the aid of feedback denoted Rx from receive unit90 (seeFIG. 4) via afeedback extractor80.Feedback extractor80 detects the mapping scheme index and forwards it tocontroller66.Controller66 looks up the corresponding mapping scheme which is to be applied indatabase78. In cases where channel parameters, e.g., channel coefficients matrix H, have to be known to employ the applied mapping scheme receiveunit90 may also send the channel parameters.Extractor80 delivers the channel parameters tocontroller66 as well asspatial multiplexing block206 and space-time coding block208. Once again, in the event of using a time-division duplexed (TDD)channel22, the feedback information, i.e., the channel parameters are obtained during the reverse transmission from the receive unit or remote subscriber unit, as is known in the art, and nodedicated feedback extractor80 is required.

The above embodiments will provide a person of average skill in the art with the necessary information to use the two metrics, minimum Euclidean distance and probability of error for making the appropriate selection of applied mapping scheme in communications systems with various multi-antenna transmit and receive units. In addition, the below examples suggest some specific implementations to further clarify the details to a person of average skill in the art. The transmit diversity coding in these examples includes space-time block coding, selection of k transmit antennas, equal gain combining and maximum ratio combining. The spatial multiplexing in these examples includes spatial multiplexing using a maximum likelihood (ML) receiver, spatial multiplexing with a linear receiver such as a zero-forcing equalizer (ZFE) receiver and minimum mean square error (MMSE) receiver and spatial multiplexing with successive canceling receiver.

At a data transfer rate r and minimum Euclidean distance d²_min,rxof the transmitted constellation, the minimum Euclidean distance for space-time block coding (stbc) is d²_min,stbcon the receive end and is expressed in terms of channel coefficients matrix H. H is an M_r×M_tmatrix where M_ris the number of receiveantennas92 and M_tis the number of transmitantennas72 known to the receiver with the Frobenius norm defined as:${H}_F:=\sqrt{\sum _{k=1}^{M_t}\sum _{m=1}^{M_r}{h_{\mathrm{km}}}^2}=\sqrt{\sum _{k=1}^{\min \left(M_t{M}_r\right)}{\mathrm{<figure-callout\; label="\lambda \; k"\; filenames="USRE040056-20080212-D00004.png,USRE040056-20080212-D00005.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}_k^{}}$
where λ_k²are the squared singular values. This allows us to write:$\begin{array}{c}{d}_{\min ,\mathrm{<figure-callout\; label="stbc"\; filenames="USRE040056-20080212-D00004.png,USRE040056-20080212-D00005.png"\; state="\{\{state\}\}">stbc</figure-callout>}}^2=\frac{{H}_F^2}{M_t}{d}_{\min ,\mathrm{<figure-callout\; label="tx"\; filenames="USRE040056-20080212-D00004.png,USRE040056-20080212-D00005.png"\; state="\{\{state\}\}">tx</figure-callout>}}^2\\ =\frac{\sum _{k=1}^{M_t}\sum _{m=1}^{M_r}{h_{\mathrm{km}}}^2}{M_t}{d}_{\min ,\mathrm{<figure-callout\; label="tx"\; filenames="USRE040056-20080212-D00004.png,USRE040056-20080212-D00005.png"\; state="\{\{state\}\}">tx</figure-callout>}}^2\\ =\frac{\sum _{k=1}^{\min \left(M_t{M}_r\right)}{\lambda }_k^2}{M_t}{d}_{\min ,\mathrm{<figure-callout\; label="tx"\; filenames="USRE040056-20080212-D00004.png,USRE040056-20080212-D00005.png"\; state="\{\{state\}\}">tx</figure-callout>}}^2.\end{array}$
Clearly, performance is sensitive only to the power in H averaged by the number of transmitantennas72, i.e., ∥H∥_F²|M_t. The computations can be carried out, e.g., incomputing block110, and more specifically insub-block114, after it is supplied with the channel H from communicationparameters computation block104 and d²_min,sxfromdatabase108.

In selection diversity one (k=1) of the M transmitantennas72 can be chosen to maximize a quality parameter such as received SNR. In this case, when data is transmitted at rate r and the minimum Euclidean distance d²_min,selof the constellation has another expression at the receive end. Let h_kbe the k-th column of H. Then the minimum Euclidean distance d²_min,selin can be written as:$d_{\min ,\mathrm{<figure-callout\; label="sel"\; filenames="USRE040056-20080212-D00004.png,USRE040056-20080212-D00005.png"\; state="\{\{state\}\}">sel</figure-callout>}}^2=\underset{k}{\max }{h_k}^2{d}_{\min ,\mathrm{<figure-callout\; label="tx"\; filenames="USRE040056-20080212-D00004.png,USRE040056-20080212-D00005.png"\; state="\{\{state\}\}">tx</figure-callout>}}^2.$
It should be noted that d²_min,sel≧d²_min,stbcsince the maximum norm of one column is always greater than the average of the norms of all the columns. Using formalisms known in the art a more direct relationship can be written as:$\begin{array}{c}{d}_{\min ,\mathrm{<figure-callout\; label="sel"\; filenames="USRE040056-20080212-D00004.png,USRE040056-20080212-D00005.png"\; state="\{\{state\}\}">sel</figure-callout>}}^2\ge \frac{{\lambda }_{\max }^2\left(H\right)d_{\min ,t}^2}{M_t}\\ \ge \frac{\sum _{k=1}^{\min \left(M_t{M}_r\right)}{\lambda }_k^2}{M_t}{d}_{\min ,\mathrm{tx}}\\ =d_{\min ,\mathrm{<figure-callout\; label="stbc"\; filenames="USRE040056-20080212-D00004.png,USRE040056-20080212-D00005.png"\; state="\{\{state\}\}">stbc</figure-callout>}}^2,\end{array}$
and also
d²_min,sel≦M_tλ_max²(H)d²_min,tx′

From the above it is clear that selection diversity is always better than space-time block coding for a given channel. Typically, antenna selection should be employed when at least some partial knowledge of H is available while space-time block coding can be used at system start-up when little or no knowledge of H is available.

For generalized transmit equal gain combining, one finds an optimal transmit vector which maximizes a quality parameter, e.g., SNR, under the constraint that the vector consists purely of phase coefficients. This vector, w, with its components corresponding to transmit signals, can be defined as:
w=[1e^iφ1. . . e^iφN−1]/√{square root over (M_r)}
The solution is found by solving for φ₁, . . . φ_N−1such that w′H′Hw is maximized. This can be done by optimization techniques well-known in the art. It is useful to recognize that:
d²_min,ege≦d²_min,mrc=d_,min,txλ_max²(H),
where mrc stands for maximum ratio combining as described below. In practice, one can set these two minimum Euclidean distances as approximately equal (d²_min,erc≈d²_min,mrc) and therefore use techniques developed for maximum ratio combining.

For generalized transmit maximum ratio combining, one can find an optimal transmit vector which maximizes a quality parameter, e.g., SNR. It should be noted that this is usually the best of such linear techniques. This vector, once again denoted w, is normalized such that ∥w∥²=1 and is found by maximizing E_sw′H′Hw/N_osubject to this normalization condition. The solution, found through linear algebra, is w=w_maxthe correct singular vector corresponding to the maximum singular value. Given this one can write d²_min,mrcas:
d²_min,mrc=d²_min,txw′H′Hw=d²_min,txλ_max²(H).
It should be noted that d²_min,mrc≧d²_min,ege≧d²hd min,sel′

When employing spatial multiplexing the computations can be carried out, e.g., bysub-block112 incomputing block110. In spatial multiplexing the type of receiveunit90 is important.

In the first example receiveunit90 is of the ML type. Let s and ŝ be the transmitted and hypothesized (received) vectors, respectively, both of dimensions M_t×1. The coefficients in these vectors come from the selected QAM constellation (with |A| points) which is assumed the same for each of transmitantennas72. The average power of the per-antenna constellation is taken to be one. Let d²_min,sdenote the minimum distance of this per antenna constellation. Let S denote the set of all |A|^M′ possible s vectors. Then we can write the minimum Euclidean distance d²_min,sm−m1the received constellation as:$d_{\min ,\mathrm{sm}-\mathrm{<figure-callout\; label="ml"\; filenames="USRE040056-20080212-D00004.png,USRE040056-20080212-D00005.png"\; state="\{\{state\}\}">ml</figure-callout>}}^2=\arg \underset{s,\hat{s}\in s}{\min }\frac{{H\left(s-\hat{s}\right)}^2}{M_t}.$
Using well-known mathematical techniques bounds and approximations can be used to simplify this expression. For example, the upper bound on d²_min,sm−m1can be defined by denoting E as the space of error vectors e where E={s−ŝ≠0|s, ŝεS}, and Ē as the space of error vectors with some of the error vectors removed therefrom as follows:$d_{\min ,\mathrm{sm}-\mathrm{<figure-callout\; label="lm"\; filenames="USRE040056-20080212-D00004.png,USRE040056-20080212-D00005.png"\; state="\{\{state\}\}">lm</figure-callout>}}^2\le \arg \underset{e\in \tilde{E}}{\min }\frac{{H\underset{\_}{e}}^2}{M_t},$
wheree is an element of Ē. Alternatively, a lower bound on d²_min,sm−m1can be defined as follows:$d_{\min ,\mathrm{sm}-\mathrm{<figure-callout\; label="ml"\; filenames="USRE040056-20080212-D00004.png,USRE040056-20080212-D00005.png"\; state="\{\{state\}\}">ml</figure-callout>}}^2\ge \frac{{\mathrm{<figure-callout\; label="\lambda \; min"\; filenames="USRE040056-20080212-D00004.png,USRE040056-20080212-D00005.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}_{\min }^{}\left(H\right)d_{\min ,s}^2}{M_t}.$

The upper bound is optimistic, meaning that it will tend to predict a minimum Euclidean distance which may be greater than it actually is in practice. The lower bound is pessimistic, meaning that it will tend to predict a minimum Euclidean distance which may be smaller than in practice. A person of average skill in the art will appreciate that, depending on the required reliability of the communication system either bound can be used. Alternatively, the two bounds can be averaged or used together in some other manner to yield the minimum Euclidean distance in spatial multiplexing with ML receiveunit90.

In another example receiveunit90 is a successive receiver, which estimates a single data stream, subtracts that stream out, estimates the next data stream, subtracts it out and so on. The performance of this type of receiver is computed based on the following algorithm:

• • 1) start with M_tdata streams and let H_i=H;
  • 2) find G, which is a ZF/MMSE inverse of H;
  • 3) let g_ibe the row of G with the minimum norm, i.e., ∥g_i∥²≦∥g_j∥²for all j≠i;
  • 4) apply g_ito H to estimate the i-th stream of data;
  • 5) subtract out the i-th stream of data and remove the i-th column of H to form a new channel coefficients matrix H_i−1;
  • 6) repeat the above steps using the new (reduced) channel coefficients matrix H_i−1.

Let {g_i}_i−1¹¹be the sequence of linear equalizers with results from the above recursion. Then we can estimate the performance of receive unit90 (assuming no feedback errors) as follows:$d_{\min ,\mathrm{<figure-callout\; label="cnc"\; filenames="USRE040056-20080212-D00004.png,USRE040056-20080212-D00005.png"\; state="\{\{state\}\}">cnc</figure-callout>}}^2=\underset{{\left(g_i\right)}_{i=1}^{M_t}}{\arg \min }\frac{d_{\min ,\mathrm{<figure-callout\; label="s"\; filenames="USRE040056-20080212-D00004.png,USRE040056-20080212-D00005.png"\; state="\{\{state\}\}">s</figure-callout>}}^2{g_i{H}_i}^2}{{g_i}^2{M}_t}$
The performance is essentially determined by linear receiver g_iwhich has the highest norm. When receiveunit90 is a ZF receiver, then the above expression simplifies to:$d_{\min ,\mathrm{<figure-callout\; label="cnc"\; filenames="USRE040056-20080212-D00004.png,USRE040056-20080212-D00005.png"\; state="\{\{state\}\}">cnc</figure-callout>}}^2=\underset{{\left(g_i\right)}_{i=1}^{M_t}}{\arg \min }\frac{d_{\min ,\mathrm{<figure-callout\; label="s"\; filenames="USRE040056-20080212-D00004.png,USRE040056-20080212-D00005.png"\; state="\{\{state\}\}">s</figure-callout>}}^2}{{g_i}^2{M}_t}.$

In yet another example, receiveunit90 is a linear receiver which first separates all the data streams using a linear equalizer (not shown) and then detects each stream independently. Let G be a linear receiver. For example, in the ZF case G=H⁺or in the MMSE case G=[HH′+I/SNR[⁻¹H′. Let g_ibe the i-th column of G. Then the minimum Euclidean distance of the receiver can be written as:$d_{\min ,\mathrm{<figure-callout\; label="ln"\; filenames="USRE040056-20080212-D00004.png,USRE040056-20080212-D00005.png"\; state="\{\{state\}\}">ln</figure-callout>}}^2=\underset{{\left(g_i\right)}_{i=1}^{M_t}}{\arg \min }\frac{d_{\min ,\mathrm{<figure-callout\; label="s"\; filenames="USRE040056-20080212-D00004.png,USRE040056-20080212-D00005.png"\; state="\{\{state\}\}">s</figure-callout>}}^2{g_i{H}_i}^2}{{g_i}^2}.$

Once again, when receiveunit90 is a ZF receiver this equation can be rewritten as:$d_{\min ,\mathrm{<figure-callout\; label="ln"\; filenames="USRE040056-20080212-D00004.png,USRE040056-20080212-D00005.png"\; state="\{\{state\}\}">ln</figure-callout>}}^2=\underset{{\left(g_i\right)}_{i=1}^{M_t}}{\arg \min }\frac{d_{\min ,\mathrm{<figure-callout\; label="s"\; filenames="USRE040056-20080212-D00004.png,USRE040056-20080212-D00005.png"\; state="\{\{state\}\}">s</figure-callout>}}^2}{{g_i}^2{M}_t},$
where the performance depends on the largest magnitude of g_i. Using a well-known property from linear algebra, namely max ∥_i∥²≦1/λ_min²(H) the above equation can used to derive a lower bound as follows:$d_{\min ,\mathrm{<figure-callout\; label="ln"\; filenames="USRE040056-20080212-D00004.png,USRE040056-20080212-D00005.png"\; state="\{\{state\}\}">ln</figure-callout>}}^2\ge \frac{{\left({\mathrm{<figure-callout\; label="\lambda "\; filenames="USRE040056-20080212-D00004.png,USRE040056-20080212-D00005.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}^2\left(H\right)\right)}_{\min }{d}_{\min ,s}^2}{M_t}.$

In this case, the performance will be influenced by the minimum singular value of H.

When the selection between diversity coding and spatial multiplexing is performed based on the minimum Euclidean distance metric as described above it is advantageous to observe the following procedure. Once the estimate of H is available and fixed transmission rate r is given the mode of operation yielding the best performance is selected by:

• • 1) computing d²_{min,Diversity}for the desired diversity coding;
  • 2) computing d²_min,SMfor the desired spatial multiplexing;
  • 3) choosing diversity coding if d²_{min,Diversity}≧d²_min,SMotherwise choosing spatial multiplexing.

Communication systems employing the metrics of the invention to select applied mapped schemes from proposed mapping schemes can be based on any multiple access technique including TDMA, FDMA, CDMA and OFDMA.

It will be clear to one skilled in the art that the above embodiment may be altered in many ways without departing from the scope of the invention. Accordingly, the scope of the invention should be determined by the following claims and their legal equivalents.

Claims (78)

1. A method of controlling a communication parameter of a channel for transmitting data between a transmit unit having a number M of transmit antennas and a receive unit having a number N of receive antennas, said method comprising:

a) providing proposed mapping schemes for converting said data into symbols and assigning said data to transmit signals TS_p, where p=1 . . . M, for transmission from said M transmit antennas;

b) obtaining a measurement of said channel at said receiver;

c) using said measurement to compute for each of said proposed mapping schemes a minimum Euclidean distance d_min,vxof said symbols when received; and

d) selecting an applied mapping scheme from said proposed mapping schemes based on said minimum Euclidean distance d_min,vx, thereby controlling said communication parameter.

2. The method ofclaim 1, wherein said proposed mapping schemes comprise modulating said data in a constellation selected from the group consisting of PSK, QAM, GMSK, FSK, PAM, PPM, CAP, CPM.

3. The method ofclaim 1, wherein said proposed mapping schemes comprise coding said data at predetermined coding rates.

4. The method ofclaim 1, wherein said proposed mapping schemes comprise at least one method selected from the group consisting of diversity coding and spatial multiplexing.

5. The method ofclaim 4, wherein said at least one method comprises diversity coding of order k ranging from 1 to M.

6. The method ofclaim 5, wherein said diversity coding is selected from the techniques consisting of space-time block coding, transmit antenna selection, Equal Gain Combining, Maximum Ratio Combining and delay diversity coding.

7. The method ofclaim 5, wherein said proposed mapping scheme comprises a random assignment of said transmit signals TS_pto a number k of said M antennas.

8. The method ofclaim 5, wherein said proposed mapping scheme comprises an assignment of said transmit signals TS_pto a number k of said M antennas based on a required minimum Euclidean distance d_min,required.

9. The method ofclaim 8, wherein said required minimum Euclidean distance d_min,requiredis related to a quality parameter of said data.

10. The method ofclaim 4, wherein said at least one method comprises spatial multiplexing of order k ranging from 1 to M.

11. The method ofclaim 10, wherein said spatial multiplexing comprises a random assignment of said transmit signals TS_pto a number k of said M antennas.

12. The method ofclaim 10, wherein said spatial multiplexing comprises an assignment of said transmit signals TS_pto a number k of said M antennas based on a required minimum Euclidean distance d_min,required.

13. The method ofclaim 12, wherein said required minimum Euclidean distance d_min,requiredis related to a quality parameter of said data.

14. The method ofclaim 10, wherein said receive unit is selected from the group consisting of maximum likelihood receivers, zero forcing equalizer receivers, successive cancellation receivers and minimum mean square error receivers.

15. The method ofclaim 1, wherein a minimum Euclidean distance d_min,txof said symbols when transmitted is stored in a database.

16. The method ofclaim 15, wherein said database is located in a unit selected from the group consisting of said transmit unit and said receive unit.

17. The method ofclaim 1, wherein said communication parameter is selected from the group consisting of data capacity, signal quality, spectral efficiency and throughput.

18. The method ofclaim 1, further comprising:

a) determining a quality parameter of said data;

b) establishing a relation between said quality parameter and a required minimum Euclidean distance d_min,requirednecessary to satisfy said quality parameter.

19. The method ofclaim 18, wherein said quality parameter is selected from the group consisting of signal-to-interference noise ratio, signal-to-noise ratio, power level, level crossing rate, level crossing duration, bit error rate, symbol error rate, packet error rate, and error probability.

20. The method ofclaim 1, wherein said transmit unit and said receive unit operate in accordance with at least one multiple access technique selected from the group consisting of TDMA, FDMA, CDMA, OFDMA.

21. The method ofclaim 20, wherein said proposed mapping schemes comprise diversity coding selected from the group consisting of space-time block coding, transmit antenna selection, Equal Gain Combining, Maximum Ratio Combining and delay diversity coding.

22. A method of controlling a communication parameter of a channel for transmitting data between a transmit unit having a number M of transmit antennas and a receive unit having a number N of receive antennas, said method comprising:

a) providing proposed mapping schemes for converting said data into symbols and assigning said data to transmit signals TS_p, where p=1 . . . M, for transmission from said M transmit antennas;

b) obtaining a measurement of said channel at said receiver;

c) using said measurement to compute for each of said proposed mapping schemes a probability of error P(e) in said symbols when received; and

d) selecting an applied mapping scheme from said proposed mapping schemes based on said probability of error P(e), thereby controlling said communication parameter.

23. The method ofclaim 22, wherein said proposed mapping schemes comprise modulating said data in a constellation selected from the group consisting of PSK, QAM, GMSK, FSK, PAM, PPM, CAP, CPM.

24. The method ofclaim 22, wherein said proposed mapping schemes comprise coding said data at predetermined coding rates.

25. The method ofclaim 22, wherein said proposed mapping schemes comprise at least one method selected from the group consisting of diversity coding and spatial multiplexing.

26. The method ofclaim 25, wherein said at least one method comprises diversity coding of order k ranging from 1 to M.

27. The method ofclaim 26, wherein said diversity coding is selected from the techniques consisting of space-time block coding, transmit antenna selection, Equal Gain Combining, Maximum Ratio Combining and delay diversity coding.

28. The method ofclaim 26, wherein said proposed mapping scheme comprises a random assignment of said transmit signals TS_pto a number k of said M antennas.

29. The method ofclaim 26, wherein said proposed mapping scheme comprises an assignment of said transmit signals TS_pto a number k of said M antennas based on a required probability of error P(e)_req.

30. The method ofclaim 25, wherein said at least one method comprises spatial multiplexing of order k ranging from 1 to M.

31. The method ofclaim 30, wherein said spatial multiplexing comprises a random assignment of said transmit signals TS_pto a number k of said M antennas.

32. The method ofclaim 30, wherein said spatial multiplexing comprises an assignment of said transmit signals TS_pto a number k of said M antennas based on a required probability of error P(e)_req.

33. The method ofclaim 30, wherein said receive unit is selected from the group consisting of maximum likelihood receivers, zero forcing equalizer receivers, successive cancellation receivers and minimum mean square error receivers.

34. The method ofclaim 22, wherein a minimum Euclidean distance d_min,txof said symbols when transmitted is stored in a database.

35. The method ofclaim 34, wherein said database is located in a unit selected from the group consisting of said transmit unit and said receive unit.

36. The method ofclaim 22, wherein said communication parameter is selected from the group consisting of data capacity, signal quality, spectral efficiency and throughput.

37. The method ofclaim 22, wherein said transmit unit and said receive unit operate in accordance with at least one multiple access technique selected from the group consisting of TDMA, FDMA, CDMA, OFDMA.

38. The method ofclaim 37, wherein said proposed mapping schemes comprise diversity coding selected from the group consisting of space-time block coding, transmit antenna selection, Equal Gain Combining, Maximum Ratio Combining and delay diversity coding.

39. A communication system with a controlled communication parameter of a channel for transmitting data between a transmit unit having a number M of transmit antennas and a receive unit having a number N of receive antennas, said transmit unit having a mapping circuit comprising:

a) a conversion unit for converting said data into symbols;

b) an assigning unit for assigning said data to transmit signals TS_p, where p=1 . . . M, for transmission from said M transmit antennas, said converting and said assigning being in accordance with proposed mapping schemes;

said receive unit comprising:

a) a channel estimator for obtaining a measurement of said channel;

b) a computing block for computing for each of said proposed mapping schemes a minimum Euclidean distance d_min,rxof said symbols when received; and

c) a selection block for selecting an applied mapping scheme from said proposed mapping schemes based on said minimum Euclidean distance d_min,vx, thereby controlling said communication parameter.

40. The communication system ofclaim 39, wherein said assigning unit comprises a diversity coding block and a spatial multiplexing block.

41. The communication system ofclaim 40, wherein said diversity coding block comprises at least one block selected from the group consisting of a space-time coding block, a transmit antenna selection block, Equal Gain Channel coding block, Maximum Ratio Channel coding block and delay diversity coding block.

42. The communication system ofclaim 40, wherein said receive unit is selected from the group consisting of maximum likelihood receivers, zero forcing equalizer receivers, successive cancellation receivers and minimum mean square error receivers.

43. The communication system ofclaim 39, further comprising a database for storing a minimum Euclidean distance d_min,txfor said symbols when transmitted.

44. The communication system ofclaim 39, wherein said computing block is selected from the group consisting of blocks for computing data capacity, signal quality, spectral efficiency and throughput.

45. The communication system ofclaim 44, further comprising a quality parameter computation block for determining a quality parameter of said data, said quality parameter being selected from the group consisting of signal-to-interference noise ratio, signal-to-noise ratio, power level, level crossing rate, level crossing duration, bit error rate, symbol error rate, packet error rate, and error probability.

46. The communication system ofclaim 45, further comprising an assessment block for establishing a correlation between said quality parameter and a required minimum Euclidean distance d_min,required.

47. The communication system ofclaim 39, said communication system operating in accordance with at least one multiple access technique selected from the group consisting of TDMA, FDMA, CDMA, OFDMA.

48. A communication system with a controlled communication parameter of a channel for transmitting data between a transmit unit having a number M of transmit antennas and a receive unit having a number N of receive antennas, said transmit unit having a mapping circuit comprising:

a) a conversion unit for converting said data into symbols;

b) an assigning unit for assigning said data to transmit signals TS_p, where p=1 . . . M, for transmission from said M transmit antennas, said converting and said assigning being in accordance with proposed mapping schemes;

said receive unit comprising:

a) a channel estimator for obtaining a measurement of said channel;

b) a computing block for computing for each of said proposed mapping schemes a probability of error P(e) of said symbols when received; and

c) a selection block for selecting an applied mapping scheme from said proposed mapping schemes based on said probability of error P(e), thereby controlling said communication parameter.

49. The communication system ofclaim 48, wherein said assigning unit comprises a diversity coding block and a spatial multiplexing block.

50. The communication system ofclaim 49, wherein said receive unit is selected from the group consisting of maximum likelihood receivers, zero forcing equalizer receivers, successive cancellation receivers and minimum mean square error receivers.

51. The communication system ofclaim 48, wherein said diversity coding block comprises at least one block selected from the group consisting of a space-time coding block, a transmit antenna selection block, Equal Gain Channel coding block, Maximum Ratio Channel coding block and delay diversity coding block.

52. The communication system ofclaim 48, further comprising a database for storing a required probability of error P(e)_req.

53. The communication system ofclaim 48, wherein said computing block is selected from the group consisting of blocks for computing data capacity, signal quality, spectral efficiency and throughput.

54. The communication system ofclaim 53, further comprising a quality parameter computation block for determining a quality parameter of said data, said quality parameter being selected from the group consisting of signal-to-interference noise ratio, signal-to-noise ratio, power level, level crossing rate, level crossing duration, bit error rate, symbol error rate, packet error rate, and error probability.

55. The communication system ofclaim 48, said communication system operating in accordance with at least one multiple access technique selected from the group consisting of TDMA, FDMA, CDMA, OFDMA.

56. A wireless communication device comprising:

a channel estimator, responsive to one or more antennas, to receive a plurality of signals associated with a communication channel, and to obtain a measurement of the communication channel;

a processing element, responsive to the channel estimator, to compute for a plurality of proposed mapping schemes a minimum Euclidean distance between symbols of the received signal(s)based, at least in part, on the channel measurement; and

a selection block, responsive to at the processing element, to select a mapping scheme from the proposed mapping schemes based, at least in part, on the computed Euclidean distance with the0ommunieationohannel, wherein the selected mapping scheme denotes how content at a remote communications device is to be applied to one or more antenna(s)associated with the remote communications device, and wherein the wireless communication device is able to provide an indication of the selected mapping scheme to the remote communications device.

57. A wireless communication device according toclaim 56, wherein the performance parameter is one or more of a measure of receive signal strength, a measure of interference, a signal-to-noise ratio(SNR), a signal-to-interference and noise ratio(SINR), a bit-error rate(BER), a packet-error rate(PER).

58. A wireless communication device according toclaim 56, wherein the channel estimator obtains a measurement of the channel coefficients matrix H characterizing the communication channel.

59. A wireless communication device according toclaim 58, wherein selection block selects an applied mapping scheme for use by a remote transmitter of the communication channel from a plurality of potential mapping schemes based, at least in part, on the measurement of the channel coefficient matrix H.

60. A wireless communication device according toclaim 58, further comprising:

a local transmitter, responsive to the selection block, to provide the indication of the selected mapping scheme to the remote communication device for application to subsequent transmission via the communication channel.

61. A wireless communication device according toclaim 56, wherein the proposed mapping schemes include one or more of modulating said data in a constellation selected from the group consisting of PSK, QAM, GMSK, FSK, PAM, PPM, CAP, CPM.

62. A wireless communication device according toclaim 56, wherein the wireless communication device is a wireless station in a wireless network including one or more antenna(e)through which downlink signals are received from remote wireless access point.

63. A wireless communication device according toclaim 56, further comprising:

a memory system to store content including executable content; and

one or more processor element(s), coupled with the memory system, to selectively access and execute at least a subset of the stored content to implement one or more of the channel estimator, computing block and selection block.

64. A wireless communication device comprising:

a channel estimator, responsive to one or more antennas, to receive a plurality of signals associated with a communication channel, and to obtain a measurement of the communication channel;

a processing element, responsive to the channel estimator, to compute for a plurality of proposed mapping schemes a probability of error of the received signal(s); and

a selection block, responsive to the processing element, to select a mapping scheme from the proposed mapping schemes based, at least in part, on the computed probability of error, wherein the selected mapping scheme denotes how content at a remote communications device is to be applied to one or more antenna(s)associated with the remote communications device, and wherein the wireless communication device is able to provide an indication of the selected mapping scheme to the remote communications device.

65. A wireless communication device according toclaim 64, wherein the performance metric is one or more of a measure of receive signal strength, a measure of interference, a signal-to-noise ratio(SNR), a signal-to-interference and noise ratio(SINK), a bit-error rate(BER), a packet-error rate(PER).

66. A wireless communication device according toclaim 64, wherein the channel estimator obtains a measurement of the channel coefficients matrix H characterizing the communication channel.

67. A wireless communication device according toclaim 64, further comprising:

a local transmitter, responsive to the selection block, to communicate the select applied mapping scheme to a remote transmitter of the communication channel for application to subsequent via the communication channel.

68. A wireless communication device according toclaim 64, wherein the proposed mapping schemes include one or more of modulating said data in a constellation selected from the group consisting of PSK, QAM, GMSK, FSK, PAM, PPM, CAP, CPM.

69. A wireless communication device according toclaim 64, further comprising:

a memory system to store content including executable content; and one or more processor element(s), coupled with the memory system, to selectively access and execute at least a subset of the stored content to implement one or more of the channel estimator, computing block and selection block.

70. A wireless communication device comprising:

a conversion unit, to receive data for wireless transmission to a remote device and to convert the received data into symbols;

an assignment unit, responsive to the conversion unit, to assign the symbols to transmit signals TS_pof the communication channel, where p=I . . . M, for transmission from M transmit antennas; and

a receive element, coupled with the conversion unit and the assignment unit, to receive an indication of a selected mapping scheme from a plurality of possible mapping schemes from a remote communication unit, wherein the conversion and assignment are performed in accordance with the select mapping scheme.

71. A wireless communication device according toclaim 70, wherein the indication of the selected mapping scheme is received from a remote wireless communication device and is selected based, at least in part, on a minimum Euclidean distance of symbols in the received signals TS_p.

72. A wireless communication device according toclaim 70, wherein the indication of the selected mapping scheme is received from a remote wireless communication device and is selected based, at least in part, on a probability of error of said symbols in the received signals TS_p.

73. A wireless communication device comprising:

two or more omnidirectional antenna(e)through which signals associated with a communication channel are received;

a channel estimator, responsive to at least a subset of the antennas, to obtain a measurement of the received communication channel;

a processing element, responsive to the channel estimator, to compute for a plurality of proposed mapping schemes a minimum Euclidean distance between symbols of the received signal(s)based, at least in part, on the channel measurement; and

a selection block, responsive to estimator and the processing element, to select a mapping scheme from the proposed mapping schemes based, at least in part, on the computed minimum Euclidean distance to, wherein the selected mapping scheme denotes how content at a remote communications device is to be applied to one or more antenna(s)associated with the remote communications device, and wherein the wireless communication device is able to provide an indication of the selected mapping scheme to the remote communications device.

74. A communication device according toclaim 73, comprising:

a local transmitter, responsive to the selection block, to provide the indication of the selected mapping scheme to the remote communication device for application to subsequent transmission via the communication channel.

75. A wireless communication device according toclaim 74, wherein the proposed mapping schemes include one or more of modulating said data in a constellation selected from the group consisting of PSK, QAM, GMSK, FSK, PAM, PPM, CAP, CPM.

76. A wireless communication device comprising:

two or more omnidirectional antenna(e) through which signals associated with a communication channel are received;

a channel estimator, responsive to at least a subset of the antennas, to obtain a measurement of the received communication channel;

a processing element, responsive to the channel estimator, to compute for a plurality of proposed mapping schemes a probability of error of the symbols of the received signal(s); and

a selection block, responsive to and the processing element, to select a mapping scheme from the proposed mapping schemes based, at least in part, on the computed probability of error, wherein the selected mapping scheme denotes how content at a remote communications device is to be applied to one or more antenna(s) associated with the remote communications device, and wherein the wireless communication device is able to provide an indication of the selected mapping scheme to the remote communications device.

77. A communications device according toclaim 76, further comprising:

a local transmitter, responsive to the selection block, to communicate the select applied mapping scheme to a remote transmitter of the communication channel for application to subsequent transmission via the communication channel.

78. A wireless communication device according toclaim 76, wherein the proposed mapping schemes include one or more of modulating said data in a constellation selected from the group consisting of PSK, QAM, GMSK, FSK, PAM, PPM, CAP, CPM.

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