Detailed Description
A carrier allocation technique for use in a multi-carrier system is described. The present carrier allocation technique selects a band of carriers or subcarriers to allocate to a user or user equipment (CE) for use thereby. In one embodiment, the allocation is performed such that carriers closer to or at the center of the band are allocated to subscriber units and CEs further away from the base station, and carriers closer to the edges of the band are allocated to CEs and subscriber units closer to the base station.
In one embodiment, the techniques described herein increase the transmitter Radio Frequency (RF) power available from the Power Amplifier (PA) of a CPE, CE, terminal, subscriber unit, portable device, or handset by exploiting the multi-carrier nature of a multi-carrier system, such as an orthogonal frequency division multiple access (OFDM) system. This technique can double or even quadruple the output power of the PA, which results in a balanced RF link design in a bi-directional communication system. In one embodiment, the technique may be employed to control PA equipment to operate at higher power while complying with adjacent channel leakage power (ACPR) transmission requirements associated with the standard (to which the present system is compliant). This may occur when the subscriber unit's power control increases the transmit power when further away from the base station after being allocated a carrier at or near the center of the band to be allocated. Thus, the techniques described herein allow for increasing or decreasing transmit power depending on the location of the user. In one embodiment, the alternative carrier approach described herein results in a 3 to 6dB power increase, which can significantly improve the RF link budget.
Such allocation methods may be used in wireless systems serving fixed, portable, mobile users or a mixture of these types of users. Note that the terms "user", "user equipment" and "subscriber unit" will be used interchangeably.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form, rather than in detail, in order to avoid obscuring the present invention.
Some portions of the detailed descriptions which follow are presented in terms of algorithms and symbolic representations of operations on data bits within a computer memory. These algorithmic descriptions and representations are the means used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. An algorithm is here, and generally, conceived to be a self-consistent sequence of steps leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like.
It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the following discussions, it is appreciated that throughout the description, discussions utilizing terms such as "processing" or "computing" or "calculating" or "determining" or "displaying" or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices.
The present invention also relates to apparatus for performing the operations herein. This apparatus may be specially constructed for the required purposes, or it may comprise a general-purpose computer selectively activated or reconfigured by a computer program stored in the computer. Such a computer program may be stored in a computer readable storage medium, such as, but is not limited to, any type of disk including floppy disks, optical disks, CD-ROMs, and magnetic-optical disks, read-only memories (ROMs), Random Access Memories (RAMs), EPROMs, EEPROMs, magnetic or optical cards, or any type of media suitable for storing electronic instructions, each coupled to a computer system bus.
The algorithms and representations presented herein are not inherently related to any particular computer or other apparatus. Various general-purpose systems may be used with programs in accordance with the teachings herein, or it may prove convenient to construct more specialized apparatus to perform the required method steps. The required structure for a variety of these systems will appear from the description below. In addition, the present invention is not described with reference to any particular programming language. It should be appreciated that a variety of programming languages may be used to implement the teachings of the invention as described herein.
A machine-readable medium includes any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computer). For example, a machine-readable medium includes read only memory ("ROM"); random access memory ("RAM"); a magnetic disk storage medium; an optical storage medium; a flash memory device; electrical, optical, acoustical or other form of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.); and so on.
Selectable carrier allocation
The disclosed alternative carrier allocation techniques are applicable to multi-carrier systems. Examples of such systems include Orthogonal Frequency Division Multiple Access (OFDMA), multi-carrier CDMA, and the like. For example, the selectable carrier allocation will be described below in terms of an OFDM system.
In one OFDM system, OFDMA is used for uplink communications to share the spectrum with common users in the same sector. In other words, the user or CE uses only a portion of the available carrier (or tones) for any given transmission. The base station assigns these carriers to users in a systematic way to avoid as much interference as possible with other users in the same sector. The decision to select a set of carriers may be based on some criteria such as, but not limited to, fading, signal-to-noise ratio (SNR), and interference.
Fig. 1A shows a frequency spectrum of one embodiment of a multi-carrier system, such as OFDM. In such systems, there are many modulated carriers (n) that occupy a certain bandwidth. For a 3GPP system, the bandwidth is 3.84 MHZ. The non-linearity in the PA mixes or modulates these tones with each other to produce cross modulation distortion (IMD) components. The dominant contribution of these IMDs is due to third-order (2f × f) and fifth-order (3f × 2f) intermodulation. The IMD produced by the wideband multi-tone signal causes the spectrum to spread energy (or spill) outside of the allocated 3.84MHz bandwidth. This is commonly referred to as spectral regrowth. Fig. 1B depicts the spectral regrowth phenomenon.
Spectral regrowth due to third order intermodulation falls in the upper and lower adjacent channels, while the fifth order intermodulation component falls in the upper and lower alternate channels. Other higher order components are generally weaker and can be ignored in most practical applications.
As mentioned above, non-linearities in PAs have many third order components and are of great interest. These components are considered ACLR power in the adjacent channel. The fifth and higher order components propagate away from the main channel and their effect is not a determining factor.
In a multi-carrier wireless system using "N" tones, the subscriber unit or CE uses only limited tones, such as "X" tones, where X is a number much smaller than N. A CE or subscriber unit using a cluster of X tones will occupy (X/N) of the total channel bandwidth. As depicted in fig. 1B, spectral regrowth due to the third and fifth order components is stronger and very important. This determines the coupled power of adjacent and alternate channels.
If a cluster around the center of the assigned channel is selected for transmission, then the dominant IMD component may fall within the channel bandwidth. Thus, these carriers may be subject to high levels of non-linear amplification and may be available for transmission at increased power levels compared to other carriers. CEs/subscriber units closer to the base station operate at lower power than CEs/subscriber units further away. Fig. 1C depicts the linear operation and IMD products generated as a function of operating power.
CEs/subscriber units far from the base station will experience larger path losses and they must operate at higher power. Operating at higher powers produces high levels of IMD components and causes spectral growth. Clusters around the center of the operating channel may be assigned to these CEs/subscriber units, thereby reducing and possibly minimizing overflow to adjacent channels while achieving higher transmit power.
Fig. 2 illustrates one embodiment of a process for allocating carriers in a multi-carrier system. The process is performed by processing logic that may comprise hardware (e.g., circuitry, dedicated logic, etc.), software (such as is run on a general purpose computer system or a dedicated machine), or a combination of both.
Referring to fig. 2, the process begins with processing logic at a base station comparing interference to adjacent channels (e.g., leakage power of adjacent channels) in a multi-carrier system with the output power of a subscriber unit as a function of the distance of the subscriber unit from the base station (processing block 201). Processing logic of the base station then selectively assigns one or more carriers to the subscriber unit based on the result of the comparison (processing block 202). In one embodiment, one or more users closer to the base station are assigned carriers closer to the edge of the operating channel band and one or more users further from the base station are assigned carriers around the center of the operating channel. Referring to fig. 1B, CE occupies the primary channel bandwidth of [ (X/N) × 3.84] Mhz for uplink transmission. The third order IMD components generated by this channel will occupy [ (X/N) × 3.84] Mhz on the upper and lower sides of the primary channel. Similarly, the fifth order IMD component will occupy the other [ (X/N) × 3.84] Mhz on both sides of the third order component. Thus, twice the primary channel bandwidth on each side of the primary channel will be occupied by a significant component of the IMD. Thus, clusters that fall within the center of the self-band {1/2[3.84- (4 primary channel bandwidth) ] } may benefit from this carrier allocation method.
Due to this allocation, dominant, undesired spectral regrowth may be restricted to lie within occupied channels of the wireless system and interference to adjacent channels may be avoided. Also, the PA of the subscriber unit can operate closer to the 1dB compression point and output higher power than conventionally used. Operation close to the compression point also improves the efficiency of the PA.
In one embodiment, the allocated carriers are Orthogonal Frequency Division Multiple Access (OFDMA) carriers. OFDMA carriers may be allocated in clusters. In another embodiment, each carrier may be a spreading code, and the multi-carrier system comprises a multi-carrier code division multiple access (MCCDMA) system.
In one embodiment, the multi-carrier system is a wireless communication system. Alternatively, the multi-carrier system is a cable system.
Fig. 3 illustrates one embodiment of a process performed by a base station for allocating band carriers in a multi-carrier system. The process is performed by processing logic that may comprise hardware (e.g., circuitry, dedicated logic, etc.), software (such as is run on a general purpose computer system or a dedicated machine), or a combination of both.
Referring to fig. 3, the process begins with processing logic receiving a communication indicating that a user intends to transmit (processing block 301). In one embodiment, the communication is a random access intention by the user to transmit data and is to be received by the base station.
In response to receiving the communication, processing logic of the base station calculates the transmit power requirements of the subscriber unit and determines whether the subscriber is near or far (processing block 302). In one embodiment, processing logic calculates the delay and path loss associated with the user and uses this information to calculate the transmit power requirement. Note that the transmit power is based on path loss and the delay provides additional information about the user equipment distance. In one embodiment, processing logic uses additional factors, such as SINR, to calculate the transmit power requirement.
Based on the calculated transmit power requirements and the determination of the proximity of the subscriber unit, processing logic assigns carriers to the subscribers (processing block 303). In one embodiment, in a multi-carrier system, each carrier is identified by an audio number, or a group of carriers is identified by a cluster number. The base station directs the user equipment to use a particular class of carriers identified by their numbers. In one embodiment, processing logic in the base station allocates carriers near the center of the band to subscriber units further from the base station and allocates carriers near the edges of the band to subscriber units closer to the base station. Processing logic may attempt to allocate more carriers closer to the edge of the band to reserve carriers for subscriber units that are not currently present that will enter the coverage area of the base station in the future, or will move from a location close to the base station to an already present subscriber unit that is located further away from the base station.
In one embodiment, to assign carriers to subscribers, processing logic in the base station assigns a priority code to each subscriber unit based on the location of the subscriber unit relative to the base station (e.g., whether the subscriber unit is far from or near the base station). The priority codes are assigned according to the transmit power requirements, which in turn depend on the path loss. The location of the CE determines the path loss. Generally, the further the CE is from the base station, the more path loss, although this is not always the case. For example, there may be a CE that is very close (to the base station) but behind a high rise building or slope, causing RF shadowing. In this case, the CE will have a large path loss. In one embodiment, the user furthest from the base station is assigned priority code #1, followed by the second furthest user by priority code #2, and so on.
Processing logic in the base station may also issue a command to the subscriber unit to use the nominal, or "z dB" extended power control range above the nominal range based on priority and carrier allocation (processing block 304). In other words, the base station issues a command to the user to indicate whether to increase or decrease its transmit power. This is a closed loop power control to tune the user's transmit power.
In one embodiment, processing logic in the base station also adjusts the power control setting for the user in a closed loop power control setting and continuously monitors the power received from the user (processing block 305). For example, if the channel characteristics change, the path loss also changes and the base station must update the transmit power of the CE.
Figure 4 illustrates one embodiment of processing performed by a subscriber unit in a multi-carrier system. The process is performed by processing logic that may comprise hardware (e.g., circuitry, dedicated logic, etc.), software (such as is run on a general purpose computer system or a dedicated machine), or a combination of both.
Referring to fig. 4, processing logic in the subscriber unit sends a notification to the base station indicating that it intends to transmit data (processing block 401). In one embodiment, the processing logic issues a random access intention to transmit data.
Processing logic in the subscriber unit receives an indication of a carrier assignment based on the location of the subscriber unit relative to the base station (processing block 402). In one embodiment, the indication is from a base station on a control channel.
In one embodiment, processing logic in the subscriber unit also receives a command from the base station to use the nominal or extended power control range (processing block 403). In one embodiment, whether the base station indicates to the subscriber unit to use the nominal or extended power control range is based on a specified priority and carrier allocation. These commands indicate to the subscriber unit that it will increase or decrease its transmit power and the selection is made based on the location of the subscriber relative to the base station.
FIG. 5 is a block diagram of an embodiment of an exemplary system. Referring to fig. 5, a base station 510 is shown communicatively coupled to a subscriber unit 520. The base station 510 comprises a power control unit 511 connected to a carrier allocator 512. Carrier allocator 512 allocates carriers of the frequency band to subscriber units, e.g., subscriber unit 520, and power control unit 511 in the system. In one embodiment, the carrier allocator 512 includes a look-up table (LUT)513 of priority codes. At a given instant, the farthest user(s) may not be active in the system. Thus, the embodiments described herein use predetermined threshold limits in the LUT to determine carrier allocation and power control.
In one embodiment, carrier allocator 512 determines spectrum priority based on information gathered from access requests made by subscriber units. The carrier allocator 512 allocates a priority to each user according to a location with respect to the base station 510 and then allocates a carrier to each user. Carrier allocator 512 allocates carriers at or near the center of the band to users furthest from the base station and allocates carriers closer to or at the edges of the band to users closest to base station 510. In one embodiment, carrier allocator 512 attempts to allocate subcarriers at the edges of the band to the nearest user and make room for potential users located further away from base station 510.
In one embodiment, rather than assigning individual priorities to users, carrier allocator 512 classifies them into priority groups. In a cell-based system, carrier allocator 512 identifies users near the center of the sector as forming a group and having a certain priority code. If it is assumed that the path loss contours are constant, users falling between certain path losses, or between these contours, form a group and are assigned a certain priority.
Carrier allocator 512 also continuously monitors the allocation of carriers used by different users in the system and dynamically reallocates carriers to users. For example, in a mobile system, both the mobile(s) and the base station continuously monitor the path loss and may perform reallocation and adaptive power control to extend the range. If the user moves closer to the base station, carrier allocator 512 changes the priority code and reallocates the sub-carriers closer to the center for other potential users. Similarly, when the user is far from the base station 510, then the carrier allocator changes the priority code and allocates the sub-carriers near the center of the band according to availability.
The priority determined by subcarrier allocator 512 is communicated to subscriber unit 520 by power control unit 511. In one embodiment, subcarrier allocator 512 sends information about the specific carriers available to the user, the priority codes on those carriers, and the power control range (nominal or extended). The transmission instructs the user to use a certain power control range according to their priority and carrier allocation. Power control unit 511 indicates to subscriber unit 520 the transmit power level it will use. In one embodiment, if subscriber unit 520 is assigned a carrier in the center of the spectrum, power control unit 511 instructs subscriber unit 520 to extend the power control range. That is, the power control unit 511 transmits a power control command to the user so that the power received at the base station 510 is at a desired level. Thus, the power control unit 511 is responsible for closed loop power control.
Subscriber unit 520 includes a power control unit 521. Power control unit 521 controls the transmit power of subscriber unit 520. That is, power control unit 521 adjusts the power transmitted from subscriber unit 520 to maintain the power received at base station 510 at a predetermined level required by base station 510. Thus, the power control unit 521 is responsible for closed loop power control.
In one embodiment, power control unit 521 processes power control commands received from the base station and determines the power control range allocated for subscriber unit 520. In one embodiment, power control unit 521 includes a nominal power control range (i to j) and an extended power control range (m to n), and if the user is assigned a subcarrier at the center of the spectrum, power control unit 521 tells subscriber unit 520 to extend the power control range. In one embodiment, the power control unit signals gain control circuitry of the subscriber unit's transmitter to extend the power control range. In one embodiment, subscriber unit 520 is responsive to a code from the base station indicating the available power control range. Subscriber unit 520 may include a look-up table (LUT) that holds the power control range and/or transmit power associated with each code received from the base station and uses that code as an index into the LUT to determine what power control range and/or transmit power is currently required.
The system maintains its ACLR, however, by allocating carriers near or at the center of the band, the power of the user is increased (e.g., 3-6 db). That is, in a system where a user transmits at 17dbm, typically at a range of 3 kilometers, the user assigned the center carrier will be able to transmit 18 or 19dbm, allowing it to potentially extend its range to 4 kilometers.
Fig. 11 is a block diagram of one embodiment of a user equipment transmitter. Referring to fig. 11, an upconverter 1101 mixes a signal to be transmitted with a signal from a local oscillator 1102 to produce an upconverted signal. The up-converted signal is filtered by a filter 1103. The filtered signal output from the filter 1103 is input to a variable gain amplifier 1104 to amplify the filtered signal. The amplified signal output from variable gain amplifier 1104 is mixed with a signal from local oscillator 1106 using up-converter 1105. The upconverted signal output from upconverter 1105 is filtered by filter 1107 and input to variable gain amplifier 1108.
Variable gain amplifier 1108 amplifies the signal output from filter 1107 based on a control signal. Variable gain amplifier 1108 and the control signal are controlled by a DSP engine 1109 that executes a power control algorithm 1121 using a priority code and power control range look-up table (LUT) 1122. The power control algorithm 1121 and the priority code and power control range LUT1122 are stored in external memory. In addition, the memory 1120 is also connected to the DSP engine 1109. In one embodiment, power control algorithm 1121 and LUT1122 are stored in external memory 1120 when power is turned off. DSP engine 1109 is also connected to external memory 1120 so that it can download code to the internal memory of DSP engine 1109. The output of DSP engine 1109 is a control signal to be input to FPGA/ASIC 1111, and FPGA/ASIC 1111 buffers and formats data output from DSP engine 1109 so that the data is readable by digital-to-analog (D/a) converter 1110. The output of ASIC 1111 is connected to the input of D/a converter 1110 to convert the control signal from digital to analog. The analog signal is input to variable gain amplifier 1108 to control the gain applied to the output of filter 1107.
The amplified signal output from the output of the variable gain amplifier 1108 is input to a power amplifier 1130. The output of power amplifier 1130 is connected to a duplexer or transmit switch 1131. the output of duplexer/TR switch 1131 is connected to an antenna 1140 for transmission therefrom.
Fig. 12 is a block diagram of one embodiment of a base station transmitter. Referring to fig. 12, DSP engine 1209 performs power control and subcarrier allocation using power control algorithm 1221 in conjunction with priority code and power control range look-up table 1222 (stored in memory) and subcarrier allocator 1240, respectively. In addition, the memory 1220 is also connected to the DSP engine 1209. The output of DSP engine 1209 is power control information embedded as control bits in the transmitted information. This transmission information is input into the FPGA/ASIC 1211, and the FPGA/ASIC 1111 buffers and formats data output from the DSP engine 1209 so that the data is readable by the D/a converter 1210. The output of ASIC 1211 is input to modem and D/a converter 1210 to modulate and convert the signal from digital to analog. The analog signal is input to an up-converter 1201.
Upconverter 1201 mixes the signal from converter 1210 with the signal from local oscillator 1202 to produce an upconverted signal. The up-converted signal is filtered by filter 1203. The filtered signal is output to a variable gain amplifier 1204 to amplify the signal. The amplified signal is output from variable gain amplifier 1204 and mixed with a signal from local oscillator 1206 using up-converter 1205. The upconverted signal output from upconverter 1205 is filtered by 1207.
The variable gain amplifier 1208 amplifies the signal output from the filter 1207. The amplified signal output from the variable gain amplifier 1208 is input to a power amplifier 1230. The output of the power amplifier 1230 is connected to a duplexer or transmit switch 1231. The output of duplexer/TR switch 1231 is connected to an antenna 1240 for transmission therefrom.
An exemplary System
Figure 6 illustrates an example system with one base station, its coverage area, and multiple users. The coverage area of the base station is divided into distance groups 1 to 4. Although not required to be so limited, there are 5 users A, B, C, D and E issuing random access intents to send data. These users are located at the physical locations depicted in fig. 6.
The spectrum is divided into subgroups numbered 1, 2, 3 and 4. The grouping is in this example based on path loss. Table 1 summarizes the group properties and transmit power requirements for each subscriber unit.
Table 1 packet and power control table
| Group number | Path loss in dB | Terminal transmit power in dBm | Spectrum priority code | Spectrum allocation | Power control range |
| 1 | ＞-100 | ＜-13 | 4 | Center +3 | Rated value | -40dBm to +17dBm |
| 2 | -101 to-115 | -12 to +2 | 3 | Center +2 | Rated value | -40dBm to +17dBm |
| 3 | -116 to-130 | +3 to +17 | 2 | Center +1 | Rated value | -40dBm to +17dBm |
| 4 | -131 to-136 | +18 to +23 | 1 | Center of a ship | Enlargement | -40dBm to +23dBm |
The allocation procedure for allocating carriers to user a is as follows. First, a user a sends a random access intention to transmit data to a base station. Second, the base station receives the request and calculates the delay and path loss for user a. Next, based on the calculation results of the delay and the path loss of the user a and table 1, the base station determines that the user a belongs to the distance group 4. The base station also determines that user a needs to transmit with spectral priority code 1. The base station then commands the use of an extended power control range and allocates carriers in the center of the spectrum. Thereafter, the base station and subscriber a adjust the power control settings in a closed loop power control mode and continuously monitor. With respect to the base station, the base station continuously monitors the signals received from the users (and calculates the time delay and path loss).
It should be noted that carriers closer to the edge or center of the band may or may not be allocated to these users than to adjacent users. For example, in the case of fig. 6, in one allocation, user E may be allocated the carrier closest to the edge of the band, followed by the second closest carrier to user D, followed by the carrier to user C, and so on, up to user a (compared to users B through E) to be allocated the carrier closest to the center of the band. However, during other allocations, one or more users may be allocated carriers closer to the edge of the band or closer to the center of the band than carriers allocated to users closer to or further from the base station, respectively. For example, in fig. 6, it is possible to assign carriers closer to the band edge to user D than to user E.
Comparison with prior art systems
Fig. 7 is a spectrum diagram of an ACLR of 45dBc for a system having a hardware platform designed for an 1800MHZ TDD wireless communication system. This amount of 45dBc is chosen because if the system is designed to be ANSI-95 compatible, then the ACLR of 45dBc must be met, and the ACLR for PCS CDMA systems is defined in ANSI-95 as 45dBc in 30 KHzRBW. To meet the ACLR of 45dB, the output power capability of the terminal is about +17 dbM.
Fig. 9 shows that for an ACLR of 33dBc, the terminal capability using the carrier allocation operation described herein is +23 dBm. One of the evolving standards, 3GPP, defines an ACLR for CE of 33 dBc.
Note that operating the user's PA closer to compression for more power causes distortion in-band. However, the performance of the system is not degraded using the method of the present invention. This fact can be seen by using the example given below.
The power control algorithm ensures that the power received by the base station from all CEs or users reaches the same level. This means that the peak to average ratio of the signal received at the base station is close to zero. Assume in this example that the carrier at the center of a cluster of channels is assigned to the farthest user and that this user meets the transmitted signal quality and SNR requirements needed for demodulation by the base station receiver. If the minimum detectable signal of the receiver is-92 dBm for a SNR of 10dB, then the receive noise floor is set to-102 dBm. If the farthest CE is operating at a TX SNR of 12dB or better and the power control algorithm sets the system so that the signal from that CE arrives at the base station at-92 dBm, the IMD components produced by that CE will be buried in the RX noise floor. All other channels see only the receive noise floor. The receiver thermal noise floor is inherent to all communication systems. Thus, the overall performance of the system is not degraded.
To increase, and possibly maximize, the output power available to the farthest terminal, a cluster in the center of the channel may be allocated. In this way, IMD products and spectral regrowth generated by the farthest user do not cause spillover to adjacent channels.
Fig. 9 shows that the terminal is capable of transmitting at an output power level of +25dBm while maintaining an ACLR of 45 dBc. This improves by nearly 8dB compared to the situation described above in fig. 7. As noted above, the PA efficiency is better when operating closer to its saturation power. Thus, it improves battery life without the cost of hardware devices. The resulting measure of the intermodulation component of the in-band channel is 14 dB. The distortion component power level is lower than the receiver SNR requirement of the 12dB requirement for the uplink in other systems.
The in-band Noise Power Ratio (NPR) typically characterizes the distortion of a multi-carrier system. FIG. 10 is a measurement of NPR when the CE is operating at a power level of +23 dBm. The NPR is about 22dB, indicating that the distortion level will be annihilated well below the thermal noise floor of the base station receiver.
Table 2 below summarizes the performance improvements achieved by the alternative carrier allocation methods described herein.
TABLE 2 comparison of Performance
| Channel power (dBm) | NPR(dB) | ACPR conventional method | ACPR-selectable carrier allocation method |
| 14 | 32 | ＞45 | ＞45 |
| 17 | 32 | 45 | ＞45 |
| 20 | 28 | 39 | ＞45 |
| 23 | 22 | 33 | ＞45 |
| 24 | 18 | - | ＞45 |
| 25 | 12 | - | ＞45 |
| 26 | 9 | - | 45 |
Conclusion
A carrier allocation method and apparatus is described which makes it possible to maximize the transmitter power of a subscriber unit or user equipment CE. In one embodiment, improvements from 3dB to 6dB can be achieved using the methods described herein to allocate OFDM audio to subscriber units or CEs.
Whereas many alterations and modifications of the present invention will no doubt become apparent to a person of ordinary skill in the art after having read the foregoing description, it is to be understood that any particular embodiment shown and described by way of illustration is in no way intended to be considered limiting. Therefore, references to details of various embodiments are not intended to limit the scope of the claims which in themselves recite only those features regarded as essential to the invention.