CA 0221~079 1997-09-09 WIRELESS LOOP SYSTEM WITH ENHANCED ACCESS
BACKGROUND OF THE INVENTION
1. Field of the invention:
The present invention relates to a wireless telephony system 10 in which the base station resource is most efficiently utilized in order to, in particular but not exclusively, replace twisted pair/wireline loop telephony with wireless telephones, therefore enhancing the economics of wireless loop access.
15 2. Brief description of the prior art:
In the prior art, the two following prior art architectures for wireless telephony systems have been exploited: distributed base stations and distributed antennas.
Distributed Base Stations Wireless telephony systems, for example cellular telephony systems, Personal Commu"icaliGn Systems (PCS), etc., basically involve 25 wireless communications between a mobile telephony user (mobile) and a central site (base station). In a wireless telephony system, the base slaliol1s are typically distributed across a serving area and are associated CA 0221~079 1997-09-09 to respective, large collocated antenna structure (tower site) to define a plurality of mutually adjacent macrocells. Each macrocell tower site provides a coverage footprint (area bounded by a contour on the earth surface formed by the intersection of the earth surface and that portion of the beam of the antenna structure above a specified minimum gain level) 5 contiguous with the other adjacent macrocells. The spacing between macrocells is principally chosen to provide the mobiles with outdoor coverage; it is accepted the mobiles' indoor coverage will be uncertain because of losses in the wireless link that arise from penetrating buildings.
A base station (sometimes abbreviated to a BTS) comprises a group of transceivers (sometimes abbreviated to TRUs) for supporting wireless communication links. For example, in the important case of a Global System for Mobiles (GSM), a transceiver is designed to support a 15 single Time Division Multiple Access (TDMA) carrier, itself capable of establishing w.;.~less Iinks to a maximum of eight simultaneous mobiles.
To support indoor mobiles from the macrocell requires a closer spacing of macrocell tower sites; the distance a link is made over is 20 decreased to provide robust enough margins to support the building penetration losses. Paradoxically this closer spacing will usually make the outdoor coverage uncertain; the closely sp~cecl macrocells will create occasional outdoor zones of excessive self interference where the building penetration loss factors are absent from the link budget.
To support both outdoor and indoor mobiles with certainty, prior art methods consists of using widely spaced macrocell tower sites for CA 0221~079 1997-09-09 outdoor coverage and operating a second set of closely spaced base stations (microcells) on differing frequencies and/or differing codes/timeslots. This second set of base stations provides the in-building capability. Used in this fashion, the base stations are said to be used in a "two layer" hierarchical cell structure, i.e. a macrocell overlay and a 5 microcell underlay. It should be reminded that the term "microcell" does not necessarily imply a hierarchical cell structure; microcells can be deployed as a single layer.
Aside from coverage, a further complicating factor is the 10 transceiver sizing, i.e. the number of transceivers required in a base station. The transceiver sizing of a base station determines (a) directly the number of mobiles the base station can simultaneously support, and (b) indirectly the total number of mobiles within the base station's coverage footprint that can be satisfactorily supported at a given grade of 15 service. Not surprisingly, transceiver sizing has a strong impact on the cost of the base station. The following Table 1 shows the relationship between the number of transceivers in a base station and the total number of mobiles in the base station coverage footprint. Table 1 shows that the number of transceivers per mobile falls as the number of mobiles 20 increases. Accordingly, a large number of mobiles in the coverage footprint provides an economy of scale and is therefore desirable. This economy of scale is usually referred to as trunking efficiency.
CA 0221~079 1997-09-09 Number of Mobiles Net Base Station Average Number of Transceiver SizeTransceivers per Mobile 0.13 0.125 0.25 0.050 0.38 0.038 0.63 0.031 0.88 0.029 1.00 0.025 1.13 0.023 ~0 In Table 1: - assume a blocking probability of 0.02;
- assume Erlang B tables;
- assume a single mobile represents 0.1 Erlangs of traffic; and - assume GSM: 8 simultaneous mobiles per transceiver.
Distributed Antennas Another prior art architecture is referred to as "distributed 20 antennas" for base stations. Commercially available distributed antennas consist of a multiplicity of small (e.g. 24 inches x 8 inches x 8 inches) RF
(Radio Frequency) repeaters all connected together and to a base station through fiber and/or coaxial cables. In such an architecture, wireless communication is required only over a small distance between the mobile CA 0221~079 1997-09-09 and the closest RF repeater, and the base station can be located at a great distance from the mobile in a non-residential district. As a consequence distributed antennas partially address the problems of in-building mobiles and base station site acquisition; the quality of wireless links to in-building mobiles is improved since the wireless links are established over a small distance, and base station site acquisition no longer needs to be in a residential district. The RF repeaters themselves are typically small enough to be mounted on overhead power lines, overhead cable TV plant or on lamp-stands. By operating many RF
repeaters in a simulcast fashion, distributed antennas can in theory be designed to cover very large geographical areas.
Some prior art, commercially available distributed antennas use pre-existing cable TV coax/fiber cables to interconnect the RF repeaters and the base station, and "share" the coax/fiber cables between wireless telephony and CA~V (Cable lV) services. Other prior art, commercially available distributed aritennas use optical fibers and coaxial cables "dedicated" to support wireless communications.
Figure 1 illusl,ates a prior art "shared" system as essentially described in Canadian patent application N~ 2,158,386 (Beasley et al.) filed on September 15,1995.
In the system of Figure 1, a macrocell tower site 101 is associated to a base station 102. Communication between the base station 102 and the Public Switched Telephone Network (PSTN) 103 is available though an interface 104.
CA 0221~079 1997-09-09 The system of Figure 1 further comprises a multiplicity of RF
repeaters 105 supported from the base station 102 through a CATV tree-and-branch coaxial cable network 106. The base station 102 is bidirectionally connected to a CATV headend 111 through a BTS-fiber interface 107 and a fiber optic cable 108. The CATV headend 111 is, in turn, bidirectionally connected to the common tree-and-branch coaxial cable CATV network 106 through a single shared fiber optic cable 109 and a shared fiber optic node 110. The RF repeaters 105 and the CATV
headend 111 coordinate so that the frequency plan on the common tree-and-branch coaxial cable network 106 and the shared fiber optic cable 109 allows them to share the "shared" resources.
Still referring to Figure 1, the RF repeaters 105 communicate with wired telephone sets such as 112 through fixed radio ports such as 114, with in-building mobiles such as 115, and/or with mobiles in vehicles such as 116.
Over and above Canadian patent application N~ 2,158,386 it is believed to be prior art to suggest that the distributed antennas coverage footprint change dynamically in response to demands for service from mobiles.
Figure 2 illustrates a prior art system using a dedicated coaxial cable 201. In the system of Figure 2, a macrocell tower site 202 is associated to a base station 203. Communication between the base station 203 and the Public Switched Telephone Network (PSTN) 204 is performed though an interface 205.
~ CA 0221~079 1997-09-09 The system of Figure 2 further comprises a multiplicity of dedicated RF repeaters 206 supported from the base station 203 through a dedicated, common tree-and-branch coaxial cable network 207. The base station 102 is bidirectionally connected to the common tree-and-branch coaxial cable network 207 through the dedicated coaxial cable 201 and a BTS-coaxial interface 208.
Still referring to Figure 2, the RF repeaters 206 communicate with wired telephone sets such as 209 through fixed radio ports such as 211, with in-building mobiles such as 212, and/or with mobiles in vehicles such as 213.
United States patent NQ 5,377,255 granted to Andrew Beasley on December 27, 1994 is an example of network as described with reference to Figure 2.
Figure 3 illusl,dtes a prior art system using dedicated fiber optic cables such as 301, 302 and 303. The system of Figure 3 comprises a macrocell tower site 304 and a number of base stations, base stations 305,306 and 307 in the illustrated example. Communication between the base stations 305, 306 and 307 and the Public Switched Telephone Network (PSTN) 308 is made through an interface 309.
The system of Figure 3 further comprises a number of dedicated fiber RF repeaters, repeaters 310, 311 and 312 in the illustrated example. More specifically, base station 305 is bidirectionally connected to the RF repeater 310 through the dedicated fiber optic cable 301 and a BTS-fiber interface 313, base station 306 is bidirectionally ~ CA 0221~079 1997-09-09 connected to RF repeater 311 through the dedicated fiber optic cable 302 and a BTS-fiber interface 314, and base station 307 is bidirectionally connected to RF repeater 312 through the dedicated fiber optic cable 303 and a BTS-fiber interface 315.
Still referring to Figure 3, the RF repeaters 310-312 communicate with wired telephone sets such as 316 through fixed radio ports such as 318, with in-building mobiles such as 319, and/or with mobiles in vehicles such as 320.
Unlike the shared coaxial cable system of Figure 1, the dedicated fiber RF repeaters of Figure 3 cannot vector sum the mobile-to-base station communications on the fiber optic cable in the same manner as can be done on a coaxial cable. The technical issue is that the RF
repeaters for coaxial cable systems can operate off a common frequency reference so that, when RF repeater-to-base station signals are summed on the coaxial cable, the vector addition of signals is reasonably controlled. For fiber optic systems the infra-red lasers used to transport RF repeater-to-base station signals are not frequency locked to a common frequency reference so that vector addition of signals gives rise to problems. Typically each RF repeater has, as illustrated in Figure 3, its own fiber optic cable to form a star network rather than the coaxial tree-and-branch network of Figure 1, or each RF repeater has its own infra-red wavelength on the fiber. This latter solution of Figure 3 is practical only for a very small number of RF repeaters (e.g. 2 to 4).
Diffficulty of Distributed Base Stations ~ CA 0221~079 1997-09-09 In microcell or macrocell distributed base station systems, the base station capacity can be modified/upgraded on an "as required" basis to meet rising demand for wireless telephony. Base station modifications/upgrades vary from:
5- adding a new base station to meet demand;
to - adding transceivers to existing base stations to meet demand.
In the case of macrocells, the cost of upgrading the base stations is alleviated by the relatively small number of macrocells; due to their large coverage footprints relatively few macrocells are required in any given serving area. However, for microcells, the cost of 15 modifications/upgrades is substantial because of the large quantity of microcells that can be involved. Even worse, microcells generally operate with a smaller net demand than macrocells so they naturally have poor trunking efficiencies. This gives the microcells poor economics.
20As a result of the poor economics of microcells, they are relatively unusual and wireless telephony is mainly focused on outdoor mobile applications.
Difficulty of Distributed Antennas In the case of distributed antennas there are limitations forced by the upstream path (i.e. the mobile to RF repeater to base station path) CA 022l~079 l997-09-09 because of noise funnelling and by the downstream path (i.e. the base station to RF repeater to mobile path) because of RF repeater capability.
On the upstream path the noise level perceived by the base station is the sum of the noise generated by all the RF repeaters 5 connected to this base station. The noise level perceived by the base station therefore depends on the number of RF repeaters connected to the distributed antennas. This is sometimes referred to as "noise funnel"
effect. A consequence of noise funnelling is the degradation of the quality of the communications between a mobile and a base station as 10 the number of RF repeaters increases. A solution consists of limiting the number of RF repeaters in the distributed antenna array; a drawback of this solution is that the coverage footprint available to the base station is correspondingly r~sl, icled. Also, since the coverage footprint is resl~ icled and the number of mobiles to be supported is in rough proportion to the 15 coverage area, the base station will be limited in transceiver sizing and, therefore, will typically operate with poor trunking efficiencies and utilization. Canadian patent application N~ 2,158,386 addresses this problem for Time Division Multiple Access (TDMA) wireless systems by implementing switching in RF repeaters in the upstream path.
On the downstream path there is the issue of capability of the RF repeaters: it is not currently possible to design a RF repeater capable of supporting an unlimited number of high powered carriers for transmission over-air, at low cost, in the small mechanical size necess~ry 25 to ease site acquisition issues. In GSM, for example, a typical capability would be to support 2-3 carriers at high power levels. This limits the base station to 3 transceivers. Thus it may be seen that the downstream ~ CA 0221~079 1997-09-09 capability of the RF repeaters also bounds the base station transceiver size and therefore the economics of the base station.
OBJECTS OF THE INVENTION
An object of the present invention is to provide a wireless telephony system capable of matching the telephony handling capabilities of a wireless base station to its associated coverage footprint so as to 10 obtain a near optimal system, i.e. to ensure that the base station resource is most efficiently utilized in the wireless telephony system. Since economically efficient use of base station resources is a major issue in replacing twisted pair/wireline loop telephony with wireless telephones, the wireless telephony system according to the invention will enhance the 15 economics of wireless loop access.
SUMMARY OF THE INVENTION
More specifically, in accordance with the present invention, there is provided a wireless telephony system presenting improved trunking efficiency and/or blocking probability, comprising a plurality of distinct distributed antenna arrays, a set of base stations, and switching 25 means for selectively connecting the base stations to the distributed antenna arrays in relation to a demand for wireless communications.
CA 0221~079 1997-09-09 Those of ordinary skill in the art will appreciate that, by selectively connecting the base stations to the distributed antenna arrays in relation to the demand, very effficient use of the base station resources is enabled.
In accordance with preferred embodiments, (a) the base stations include respective transceiver units, (b) the switching means comprises means for selectively switching the transceiver units of the base stations between the distributed antenna arrays in relation to the demand for wireless communications, (c) the transceiver units of the base stations comprise one transceiver unit permanently connected to each distributed antenna array, (d) each distributed antenna array comprises a hybrid optical fiber/coaxial cable network, dedicated or shared, (e) the wireless telephony system further comprises at least one macrocell including at least one repeater/antenna site, and the switching means comprises means for selectively switching the transceiver units of the base stations between the distributed antenna arrays and the at least one macrocell in relation to the demand for wireless communications, (fl the distributed antenna arrays, and eventually the macrocell(s), have respective coverage footprints associated to regions with different busy hours, and (g) the transceiver units of the base stations comprises transceiver units shared between a plurality of said distributed antenna arrays to define a multi-layer network of distributed antenna arrays.
In accordance with another preferred embodiment of the present invention, the distributed antenna arrays have respective coverage footprints, and the switching means comprises (a) means for connecting one transceiver unit of the base stations to the distributed CA 022l~079 l997-09-09 antenna array having the coverage footprint in which a calling or called mobile subscriber is situated and, when the mobile subscriber is roving from one coverage footprint to the another coverage footprint during the call, means for connecting the same transceiver unit to the distributed antenna array having the above mentioned other coverage footprint, whereby the roving mobile subscriber is connected to the same transceiver unit during all the duration of the call even when the roving mobile subscriber passes from one coverage footprint to the other.
In accordance with another aspect of the invention, there is provided a wireless telephony system presenting improved trunking efficiency and/or blocking probability, comprising a plurality of macrocells each comprising at least one repeater/antenna site, a set of base stations, and switching means for selectively connecting the base stations to the macrocells in relation to a demand for wireless communications.
Preferably, the base stations include respective transceiver units, and the switching means comprises means for selectively switching the transceiver units of the base stations between the macrocells in relation to the demand for wireless communications.
Further in accordance with the present invention there are provided:
- a distributed antenna array comprising a network of RF repeaters producing a set of measured upstream data, and means for computing the location of a mobile within the array from the set of measured upstream data, wherein the measured upstream CA 022l~079 l997-09-09 data comprise signal quality and channel frequency at a specific time epoch;
- a wireless telephony system comprising a plurality of distributed antenna arrays and a set of base stations, wherein the distributed antenna arrays include RF repeaters comprising means for supporting, for the base stations, a hierarchical cell structure;
- a wireless telephony system comprising a plurality of distributed antennas including RF repeaters, a set of base stations, and means for selectively connecting the base stations to the distributed antenna arrays in relation to a demand for wireless communications, wherein the RF repeaters of the distributed antenna arrays comprise means for supporting, for the base stations, a hierarchical cell structure; preferably, the wireless telephony system further comprises means for controlling the switching means in relation to the location of a mobile user and a channel frequency and timeslot required.
The objects, advantages and other features of the present invention will become more apparent upon reading of the following non restrictive descli~.lion of a preferred embodiment thereof, given by way of example only with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
~ CA 0221~079 1997-09-09 In the appended drawings:
Figure 1, which is labelled as "prior art", is a schematic diagram of a "shared" wireless telephony system comprising a macrocell tower site, a base station, and a distributed antenna array including a multiplicity 5 of RF repeaters supported from the base station through a BTS-fiber interface, a fiber optic cable, a CATV headend, a single shared fiber optic cable, a shared fiber node and a CATV tree-and-branch coaxial cable network;
Figure 2, which is labelled as "prior art", is a schematic diagram of a wireless telephony system comprising a macrocell tower site, a base station, and a distributed antenna array comprising a multiplicity of dedicated RF repeaters supported from the base station through a BTS-coaxial interFace, a dedicated coaxial cable, and a dedicated common 15 tree-and-branch coaxial cable network;
Figure 3, which is labelled as "prior art", is a schematic diagram of a wireless telephony system comprising a macrocell tower site, a number of base stations, and a distributed antenna array comprising a 20 multiplicity of dedicated fiber RF repeaters supported from the base stations through BTS-fiber interfaces and dedicated fiber optic cables;
Figure 4 is a schematic diagram of a basic architecture for wireless telephony system according to the invention;
CA 022l~079 l997-09-09 Figure 5 is a schematic functional diagram, for a TDMA
wireless telephony system, showing the downstream path of a dedicated hybrid fiber-coax network underlay;
Figure 6 iS a schematic functional diagram, for a TDMA
5 wireless system, showing an u~ alll path of the dedicated hybrid fiber-coax network underlay of Figure 5;
Figure 7 is a schematic functional diagram, for a TDMA
wireless system, showing an upstream path of the dedicated hybrid fiber-10 coax network underlay of Figure 5;
Figure 8 is a variant of the schematic functional diagram of Figure 6, in which an additional base station has been added to support the RF repeaters with new carrier frequencies/codes in the downstream 1 5 path;
Figure 9 is a variant of the schematic functional diagram of Figure 7, in which an additional base station has been added to support RF repeaters with new carrier frequencies/codes in the upstream path;
Figure 10 is a schematic block diagram showing the concept of connecting many hundred of distributed antenna arrays to respective base stations;
Figure 11 is a block diagram showing, to improve trunking efficiency, the use of a switch matrix in a wireless telephony system CA 0221~079 1997-09-09 between a set of base stations and a plurality of distributed antenna arrays;
Figure 12 is a variant of the block diagram of Figure 11, further comprising a macrocell connected to the base stations through the switch 5 matrix;
Figure 13 illuslldles a re-arrangement of the block diagram of Figure 11, in which a single fixed base station is permanently connected to and shared over a multiplicity of distributed antenna arrays to thereby 10 create a multi-layer network of distributed antenna arrays;
Figure 14 is a variant of the block diagram of Figure 11 in which the switch matrix connects a same base station to a mobile roving from one distributed antenna coverage footprint to the other; and Figure 15 is a schematic diagram showing a macrocell overlay, a microcell underlay, a outdoor microcell extending a macrocell, and an indoor microcell extending a macrocell in a building.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In the different Figures of the appended drawings, identical elements are identified by the same reference numerals.
~ CA 0221~079 1997-09-09 The invention is primarily, but not exclusively, concerned with dedicated networks that utilize fiber optic and coaxial cables for TDMA
wireless telephony systems. The invention relates to matching base station transceiver size to coverage footprint using distributed antenna arrays, so that large trunking efficiencies are achieved. The invention specifically addresses the problem of modifying/upgrading the wireless telephony system as required to meet increasing demand for service from mobiles.
Figure 4 shows the basic architecture of a wireless telephony system according to the invention.
The wireless telephony system of Figure 4 comprises a plurality of base stations such as 402 and 403. For the purpose of simplifying the drawings, only two base stations are shown in Figure 4. It should however be kept in mind that it is within the scope of the present invention to use a number of base stations greater than 2.
Bidirectional communication between the base stations 402 and 403 and the Public Switched Telephone Network (PSTN) 404 is ensured by a PSTN interface 405 well known to those of ordinary skill in the art.
A macrocell tower site 406 is provided with a RF repeater 407 to establish a bidirectional communication between the macrocell tower site 406 and mobiles in vehicles such as 408. As illustrated, the macrocell RF repeater 407 is supported from either base station 402 or 403 through a switch matrix 409, and a BTS-fiber or coax interface 432 ~ CA 0221~079 1997-09-09 depending on the type of link (optical fiber or coaxial cable) between the interface 432 and the RF repeater 407. In Figure 4, the macrocell is identified with wide area roaming, i.e. mobiles in vehicles such as 408.
The wireless telephony system of Figure 4 further comprises dedicated optical fiber runs such as 411 and 412 used in a star configuration with dedicated coaxial cable networks such as 413 and 414 on one end of each optical fiber run 411 and 412.
The other end of the optical fiber run 411 is bidirectionally connected to the switch matrix 409 through a BTS-fiber interface 430. In the same manner, the other end of the optical fiber run 412 is bidirectionally connected to the switch matrix 409 through a BTS-fiber interface 431.
As shown, each coaxial cable network 413,414 is installed in a tree-and-branch configuration. The optical fiber run 411 is connected to the corresponding tree-and-branch configured coaxial cable network 413 through a dedicated fiber node 415. In the same manner, optical fiber run 412 is connected to the corresponding tree-and-branch configured coaxial cable network 414 through a dedicated fiber node 416.
A multiplicity of dedicated coaxial RF repeaters 417 operate off the coaxial cable network 413. In the same manner, a multiplicity of dedicated coaxial RF repe~ters 418 operate off the coaxial cable network 414. The RF repeaters 417 can be supported by either the base stations 402 or 403 depending on the switching state of the switch matrix 409. In the same matter the RF repeaters 418 can be supported by either the base stations 402 or 403 depending on the switching state of the switch ~ CA 0221~079 1997-09-09 matrix 409. Similarily, RF repeater 407 can be supported by either the base stations 402 or 403 depending on the switching state of the switch matrix 409. Again, to simplify the drawings, Figure 4 arbitrarily shows only two fiber runs 411 and 412 and two coaxial cable networks 413 and 414. It is obviously within the scope of the present invention to provide 5 a number of optical fiber runs and coaxial cable networks larger than two.
Still referring to Figure 4, each RF repeater 417 communicates bidirectionally with respective in-building wired telephone sets such as 419 through fixed radio ports such as 420 and 421, and with in-building mobiles such as 422. In the same manner, each RF repeater 418 communicates bidirectionally with respective in-building wired telephone sets such as 424 through fixed radio ports such as 425 and 426, and with in-building mobiles such as 427. It should be noted that, in practice, it is typical to fix allocate at least one t~a"sceiver of the base stations to each distinct coverage zone (e.g. to the three zones supported by BTS-fiber interfaces 430, 431 and 432). Consequently, the switch matrix 409 of Figure 4 does not exclude fix assignment of base station transceivers to coverage zones, though in general its purpose is to dynamically allocate them to coverage zones according to demand.
Accordingly, the wireless telephony system of Figure 4 is characterized as follows:
- it comprises a hybrid of dedicated optical fiber runs and dedicated coaxial cable network;
' CA 0221~079 1997-09-09 - a switch matrix controls connections between the base staliGns/transceivers and the different repeaters. This enables more efficient use of the base station equipments in relation to the demand for wireless communications;
- the wireless telephony system of Figure 4 is a multi-layer system: a macrocell overlay capable of supporting wide area roaming (e.g. vehicular mobiles), and a microcell underlay comprising RF Repeaters on less sophisticated sites such as telephone poles, the wire strand between the poles, lamp-stand, etc. The macrocell overlay may use a unique set of codes/frequencies while the distributed antenna arrays of the microcell underlay are preferably simulcasted.
Figure 5 is a schematic functional diagram of an example of dedicated fiber-coax network underlay usable for a TDMA wireless telephony system as illustrated in Figure 4 to support base station to subscriber (downstream path) communications. Figure 5 shows the coverage zone or footprint 501 of the macrocell tower site 406 and the respective coverage zones or footprints 502,503,504,505,506, 507 and 508 of RF repeaters 517, 515, 516, 523, 519, 520 and 521.
A communication signal from a base station such as 402 or 403 is supplied to two optical fiber runs 510 and 511 through a BTS-fiber interface such as 430 or 431. In Figure 5, the switch matrix 409 is not 25 shown and the BTS-fiber interface is identified, as a non limitative example, as an E/O (electrical to optical) converter 512 and a beam splitter 513. More specifically, the electrical communication signal from ~ CA 0221~079 1997-09-09 the base station is converted to an optical communication signal by E/O
converter 512 and is divided into two separate signals supplied to the two fiber runs 510 and 511, respectively, by splitter 513. The optical communication signal on optical fiber run 510 is supplied to dedicated coaxial RF repeaters 515 and 516 through a dedicated fiber node 525 and a network of coaxial cables 514. The dedicated fiber node 525 comprises a fiber node RF repeater 517 and a fiber-coaxial interface device 518. RF repeaters 517, 515 and 516 illuminate coverage zones or footprints 502, 503 and 504, respectively. In the same manner, the communication signal on the optical fiber run 511 is supplied to dedicated coaxial RF repeaters 519, 520 and 521 through a dedicated fiber node 526 and a network of coaxial cables 527. The dedicated fiber node 526 includes a fiber node RF repeater 523 and a fiber-coaxial interface device 524. RF repeaters 523,519,520 and 521 illuminate coverage zones 505, 506, 507 and 508, respectively. It should be pointed out here that the RF
repeaters 417 and 418 are typically simulcasted (emit and receive simultaneously the same signal) as is conventional for distributed antennas.
Figures 6 and 7 are schematic functional diagrams of the dedicated hybrid fiber-coax network underlay of Figure 5 supporting subscriber to base station (upstream path) communications for a TDMA
wireless telephony system.
In Figure 6 (corresponding to time epoch T1), wireless communication signals from coverage zones 502, 504, 507 and 508 and mobiles 604 and 605 are received by RF repeaters 515, 519 and 520 and is transmitted to the optical fiber runs 510 and 511 through the dedicated ' CA 0221~079 1997-09-09 coaxial cable networks 514 and 527 and the dedicated fiber nodes 525 and 526. Selection of the RF repeaters in the upstream path is made in the RF repeaters themselves in relation to the quality (strength, signal-to-noise ratio, etc.) of the communication signals received by the various RF
repeaters. Of course, the selected RF repeaters (repeaters 515, 519 and 520 in the example of Figure 6) are simulcasted.
The optical signals on the fiber runs 510 and 511 are converted by respective O/E (optical-to-electrical) converters 601 and 602 into electrical signals which are combined into a single electrical signal by a combiner 603. The combined signal is applied to a base station such as 402 or 403. Converters 601 and 602 along with combiner 603 form a BTS-fiber interface such as 430 or 431.
Referring now to Figure 7, corresponding to time epoch T2, wireless communication signals from coverage zones 502, 503, 505 and 508 and mobiles 701 and 702 are received by RF repeaters 515,519 and 520 and is transmitted to the optical fiber runs 510 and 511 through the dedicated coaxial cable networks 514 and 527 and the dedicated fiber nodes 525 and 526. Again, selection of the RF repeaters in the upstream path is made in relation to the quality (strength, signal-to-noise ratio, etc.) of the communication signals received by the various RF repeaters. Of course, the selected RF repeaters (repeaters 515, 519 and 520 in the example of Figure 7) are simulcasted.
Again, the optical signals on the fiber runs 510 and 511 are converted by the respective O/E (optical-to-electrical) converters 601 and 602 into electrical signals which are combined into a single electrical ' CA 0221~079 1997-09-09 signal by the combiner 603. The combined signal is applied to a base station such as 402 or 403. Converters 601 and 602 along with combiner 603 form a BTS-fiber interface such as 430 or 431.
As indicated in the foregoing description, connectivity of the RF
5 repeaters to the base station on the upstream path depends on the signal quality (e.g. signal strength, signal-to-noise ration, etc.) as measured at the RF repeaters. For example if a RF repeater does not receive a good quality signal from a subscriber on the appropriate time slot and frequency, it will disconnect itself from the upstream fiber-coax network 10 for wireless communication purposes and hence will not form part of a noise funnel. Only those RF repeaters that are estimated to receive a good quality signal from a subscriber on the appropriate time slot and frequency, will connect themselves to the upstream fiber-coax network for wireless communication purposes.
Assuming RF repeaters with three (3) carrier GSM capability, as an example, in any given time epoch only three (3) mobiles can be signaling within the distributed antenna array. Therefore the nominal number of RF repeaters connected to the upstream path for signaling 20 purposes would be three (3), and the nominal noise funnel size would be three (3) regardless of the total number of RF repeaters in the distributed antenna array. Thus the system does not have undue restrictions on the total number of RF repeaters and hence on the total coverage footprint of the distributed antenna array.
It should be noted that selective connection of RF repeaters to an upstream path implies that each RF repeater handles communications ' CA 0221~079 1997-09-09 with the mobile on a "per channel" basis: i.e. the RF repeater cannot be a broadband RF repeater but must be channel selective for upstream purposes. Thus the RF repeaters of Figures 5-9 are aware of the signal quality in their locale on both a channel and timeslot basis. This information can be sent over the hybrid optical fiber-coaxial cable network 5 back to the base station via conventional means such as a simple data link, where it allows the location of the mobile using the channel frequency and li",eslot to be determined to some precision. For example if the received signal strength is the RF repeater's criteria for signal quality, it becomes possible to triangulate the location of the mobile from 10 the data set of received signal strength measurements from nearby RF
repeaters and hence locate the mobile to some fraction of a RF repeater's coverage range, for example to within half a nominal coverage radius.
Since the RF repeater may have a coverage range of the order of 200 meters, the location of the mobile can be determined to within 100 1 5 meters.
The ability to combine upstream data link from the RF repeaters with their channel selective, upstream switching criteria, enables the creation of a number of useful location dependent services, for example 20 the ability to bill the mobile subscriber according to location ("home-zone"
billing, "fare-zone billing", etc.) and is import in some implementations of the switch matrix.
Another characteristic of Figures 5-9 that should be noted is 25 that they support both frequency hopped and non-frequency hopped configurations of a GSM wireless system. The GSM wireless system can be set so that the over-air wireless communications changes frequency ' CA 0221~079 1997-09-09 periodically ("frequency hopped1') or stays constant once the call is setup ("non-frequency hopped"). Frequency hopping provides certain well known advantages: increased performance under interference limited conditions and protection against fades in the wireless signal. In a broadband RF repeater there is little issue for the distributed antenna in 5 supporting frequency hopping since there are no narrowband components within the RF repeater. When the communications are channelized on the upstream path, as described hereinabove, frequency hopping is more difficult. Frequency hopping is handled by constraining the base station and mobile to frequency hop only over the channels 10 supported by the RF repeater. For example, if the RF repeater in a distributed array support wireless communications at just three RF
channels (say, 1.901 GHz, 1.906 GHz and 1.915 GHz), then the GSM
wireless system would be programmed to support frequency hopping only over the channels represented by 1.901 1.906 and 1.915 GHz. As a 15 consequence the mobile user constantly shifts operating channel, but the RF repeater can be designed as if the mobile user was fixed, i.e. the RF
repeater does not need to dynamically reconfigure to support the frequency hopping mobile. However if frequency hopping is to be supported, the RF repeater typically does need a priori knowledge of the 20 hop pattern to be able to keep proper track of the location of a mobile user.
The wireless loop system as described in the foregoing description:
- has no significant upstream distributed antenna limitations due to noise funneling;
' CA 0221~079 1997-09-09 - is limited by the downstream capability of the RF
repeaters; thus the trunking effficiency and utilization of the base station is constrained; and - is well suited to being a microcell underlay because the RF repeaters can be spaced closely together to enhance the in-building penetration capability of the wireless communications.
Furthermore, the above described wireless telephony system can support "as required" modifications/upgrades to provide more base station capacity by:
- physically changing the fiber optic cabling for the base station to subscriber (mobile) signaling (downstream path) as illustldted in the appended drawings by the changes in optical fiber runs from Figure 6 to Figure 8 and similarly for the subscriber to base station signaling as illusl,ated by the changes in fiber runs from Figure 7 to Figure 9 (Note that these changes all occur at the base station site, which makes the changes easy and quick to do); and - commanding half the RF repeaters of Figures 8 and 9 to use new over-air carrier frequencies and/or codes, e.g.
zones 502, 503 and 504 simulcast but at a distinctly different set of channel frequencies than simulcasting zones 505, 506, 507 and 508; and ' CA 0221~079 1997-09-09 - inserting another base station (as illusl,aled in Figures 8 and 9, base stations 402 and 403 are respectively connected to the fiber runs 510 and 511 through the E/O (electrical to optical) converters 801 and 802) to support the RF repeaters with the new carrier frequencies and/or codes in both the downstream and upstream paths.
This method of upgrading is distinct from shared systems; in shared systems it is unacceptable to physically re-organize fiber optic cables because of the impact on the other (e.g. CATV) services. In 10 shared systems new frequencies must be allocated to transport signals on the fiber optic and coaxial cables to the RF repeaters. Thus, in shared systems, the RF repeaters need to be frequency agile at the interface to the coax as well as over-air, to allow the transport frequencies to be re-specified.
The system of Figures 8 and 9 can be considered from the viewpoint of a multiplicity of distributed antenna arrays, each operating independently of the other arrays but each limited by the downstream capability of the RF repeaters to some finite base station sizing (e.g. 3 20 transceivers).
By using fiber optic cables such as 510 and 511, it becomes feasible to create a distributed antenna coverage footprint physically distant from the base station. For GSM, a nominal maximum distance of 25 35 km is possible; more feasible is 20km distance. Thus a base station site conceptually could be using dedicated hybrid optical fiber/coaxial cable network to support wireless telephony for a 20 km radius from a CA 0221~079 1997-09-09 downtown city core. Given a high density of mobiles in such an environment, the 3 transceiver sizing will equate to a relatively small coverage footprint (say 1-8 square kilometers). Thus there may need to be many hundreds of distributed antenna arrays connected to the base station site as indic~tecl in Figure 10. To keep the example concrete we will assume 1000 distributed antenna arrays connect to the base station site.
This concept is illustrated in Figure 10 which omits the switch matrix as a means of relating that concept to prior art. Figure 10 shows a number (for example 1000) of distributed antenna arrays such as 1001, 1002, 1003 and 1004, each operating on frequencies and/or codes different from the frequencies and/or codes of the neighboring distributed antennas that abut (frequencies can be re-used by non-neighbouring arrays, as is conventional in cellular-like systems). Thus handover at the distributed antennas boundaries such as 1005, 1006, 1007 and 1008 is carried out by conventional means (not shown). Each array is supported by a base station such as 1009, 1010, 1011 and 1012 each sized for three (3) transceivers such as 1013 (referred to as TRU in the appended drawings).
The system iJlustrated in Figure 10 is equivalent to a single macrocell site with, to still keep the same example, 1000 sectors. This distinguishes from the prior art in the following respects:
- A "normal" site might have 3 or 7 and in extreme cases some w;,~less technologies might operate 20 sectors. By increasing ' CA 0221~079 1997-09-09 the number of sectors by a factor of 50-300, different economy scales apply.
- A sector in a normal macrocell is defined by the coverage area or footprint supported from an antenna mounted at the macrocell tower site: there is only a limited number of adjustments that can be made to vary the shape and size of the coverage footprint of an antenna. Thus all sectors in a normal macrocell tend to be of roughly constant area. In Figure 10 the coverage zones of the distributed antenna arrays can vary in coverage area or footprint according to the density and demands of subscribers so that the correct sizing of transceivers (TRUs) for the distributed antenna array is three (3). A distributed antenna array can have the shape and size of its coverage zone varied with precision by adding or removing RF repeaters. The distributed antennas of Figure 10 can therefore be modified to define respective coverage zones that are consta,)l in demand for capacity to serve subscribers, not of constant area. Subscriber demand for service is conventionally measured in Erlangs. To maintain the constant capacity definition, the distributed antenna arrays are modified/upgraded as discussed previously.
Figure 11 shows the basic method of improving trunking effficiency, using the switch matrix 409 of Figure 4. In Figure 11, a single base station transceiver as 1101, 1102, 1103, 1104 is allocated to respective distributed antenna arrays 1105,1106, 1107 and 1108. The remaining base station transceivers such as 1109, 1110, 1111, 1112, CA 0221~079 1997-09-09 1113, 1114 and 1115 are allocated through the switch matrix 409 to a distributed antenna array whenever the demand within this distributed antenna array starts to exceed the capacity of the fixed base station transceiver such as 1101,1102, 1103 or 1104.
For example, the switch matrix 409 can be formed of an array of electronic switches (not shown) and/or a computer or microprocessor (not shown). The computer or microprocessor is connected to all the base station transceivers 1101 -1104 and 1109-1115 to monitor the demand for wireless communications on each distributed antenna array 1105-1108 and whenever this demand exceeds the capacity of the base station transceiver or transceivers already connected to this distributed antenna array the computer or microprocessor commands the electronic switches to connect another base station transceiver to that particular distributed antenna array for that particular time epoch. In the same manner, when the demand for wireless communications on one distributed antenna array 1105-1108 is lower than the capacity of the base station transceiver or transceivers already connected to this distributed antenna array the computer or microprocessor commands the electronic switches to disconnect at least one base station transceiver from that particular distributed antenna array for that particular time epoch; the disconnected base station transceiver(s) is then available for connection to other distributed antenna arrays in accordance with the demand. Of course, when the demand for wireless communications on one distributed antenna array 1105-1108 is lower than the capacity of the base station transceiver or transceivers already connected to this distributed antenna array, it is not necessary to disconnect immediately the unnecess~ry base station transceiver(s) from that particular ' CA 0221~079 1997-09-09 distributed antenna array; identification of the unnecessary base station transceiver(s) can be stored in predetermined memory addresses of the computer or microprocessor to indicate that this base station transceiver(s) is available for connection to other distributed antenna arrays in accordance with the demand and the switching is performed 5 only when required.
It should be pointed out that, in the embodiment of Figure 11, each distributed antenna array 1105, 1106, 1107 and 1108 is limited to the 15 Erlangs maximum capacity, and there is no dynamic changing of 10 the distributed antenna coverage footprints. This distinguishes over the prior art associated with dynamically changing the distributed antenna footprints to match a constant transceiver resource to demand.
Dynamically changing the distributed antenna footprints is relatively straighfforward in a shared system where the distributed antenna arrays 15 can be re-arranged by changing the fiber-coax transport frequencies of the individual RF repeaters (i.e. frequency agility on the coax exists). In the dedicated hybrid optical fiber-coaxial cable network of the invention, the fiber-coax transport frequencies may be fixed to save costs in the RF
repeaters. Consequently dynamic re-arrangement of the RF repeaters 20 becomes unattractive. The present invention keeps the configuration of the distributed antenna arrays fixed on a minute-to-minute basis, but the configuration of the distributed antenna arrays is easily modifiable on a month-to-month basis. By avoiding dynamic changes in the distributed antenna coverage footprints, continuity of communication for the 25 subscriber, mobile or not, is enhanced since calls no longer drop due to the reconfiguration of RF repeaters from one coverage zone to another while a call is in progress.
' CA 0221~079 1997-09-09 Figure 11 shows a system in which the trunking effficiencies are greatly improved; analysis indicates a 40% improvement which can be used to reduce the total number of base stations and/or transceivers or, by using the switch matrix 409 and keeping the number of base station transceivers fixed, to improve the call blocking probabilities, or a 5 combination of the two. Reduction of the total number of base station transceivers reduces accordingly the cost of the wireless telephony system. Improvement of the call blocking probabilities is attractive if the wireless telephony system is to compete against wireline networks having excellent blocking probabilities.
A somewhat larger improvement in trunking efficiency may arise because the wireless telephony system of Figure 11 provides coverage to such a large area. Base station capacity is driven by the peak demands ("busy hour"), and for a small serving area a base station 15 tends to see a constant busy hour. For example a base station serving an industrial estate will see busy hour associated with office work, say 11:00 in the morning, whereas a base station serving a predominately residential district will see a busy hour associated with family usage, say 7:00 in the evening. For the serving area represented by Figure 11, both 20 residential and industria! areas will be captured within the net coverage footprint. This results in a more economically effficient network. For example the "residential" areas will have surplus transceiver capacity at 11:00 in the morning which can be used to help handle the office busy hour trafffic, and the "offfice" areas will have surplus transceiver capacity 25 at 7:00 in the evening which can be used help handle the residential busy hour trafffic. Thus the net effect of deliberately capturing a variety of locale dependent busy hours via the switch matrix is to reduce the 'CA 0221~079 1997-09-09 quantity of transceivers even more than trunking efficiency alone considerations imply. To take maximum advantage of this effect, an overlay macrocell base station, which would deal with the busy hours associated with office-home commuters (not shown), should also use base station transceivers (TRUs 1109-1115) made available via the 5 switch matrix 409. This concept is shown in Figure 12 in which a single base station transceiver 1201 is permanently connected to the macrocell tower site 1202. The other base station transceivers 1109-1115 can be connected on demand to the macrocell through the switch matrix 409.
10Figure 13 shows a re-arrangement of Figure 11 in which a single fixed base station transceiver such as 1301 or 1302 is shared over a multiplicity of distributed antenna arrays, albeit by the reduction in total capacity available to the wireless loop system. More specifically, single fixed base station transceiver 1301 is shared over distributed antenna 15arrays 1303 and 1305 to form a distributed simulcasting antenna array 1305, and single base station transceiver 1302 is shared over distributed antenna arrays such as 1306 and 1307 to form another distributed simulcasting antenna array 1308. This is equivalent to creating a multi-layer system using just the distributed antenna arrays: effectively there is 20 created a hierarchy of distributed simulcasting arrays.
In Figure 13, the coverage zones such as 1303 and 1304 need not be physically adjacent: they could conceptually be at either ends of a very large city. In such a case, coverage zone 1305 would also be 25 separated in two physically distinct zones - that for wireless purposes -overlays 1303 and 1304. This can be advantageous, for example if the ' CA 0221~079 1997-09-09 physically distinct coverage zones 1303 and 1304 have different busy hours.
In a GSM wireless system the TRU 1301 in Figure 13 could be the "base carrier" TRU. In a GSM system, call set up, initialization, and much of the call hand off process are handled by the base carrier TRU
which can also direct calls after setup to another TRU. This allows the following implementation of the switch matrix:
- Regardless of whether the call is initiated by the mobile or by the PSTN, the GSM system will automatically direct the call setup to the base carrier TRU which serves the area the mobile is located in. For example, a mobile in location 1304 will call set up through base carrier TRU 1301.
-The base carrier TRU 1301 will co~ ~mand the mobile to communicate on a specific channel frequency and timeslot, according to a predetermined algorithm. The base carrier TRU can also command the switch matrix to connect a TRU which support that channel frequency to coverage zone 1304, for that timeslot. To do this it is essential that the location information, available from the RF repeater data link, ~ssociqtes the mobile requesting service to coverage zone 1304 and not to coverage zone 1303 which is also served by the base carrier TRU 1301.
Thus the switch matrix is controlled by both the base carrier TRU 1301, which issues requirements on channel frequency and timeslot, and the locating system of the hybrid optical fiber-' CA 0221~079 1997-09-09 coaxial cable network which associates the requirement to a specific coverage area.
As an example assume that TRU number 1112 supports the required channel frequency and is connected to coverage zone 1304 via the switch matrix 409 during timeslot 5, for both upstream and downstream communications only. This still allows TRU 1112 to serve other coverage zones on other timeslots i.e. the TRU resource has been effficiently demand assigned to coverage zone 1304 as we require. As a practical matter it is desirable that TRU 1112 be associated with a constant channel frequency i.e. TRU 1 112 actually supports a multiplicity of non-adjacent coverage zones that share the same frequency plan. For example zones 1304 and 1307 may share the same frequency plan if they are physically non-adjacent. Thus TRU 1112 can be allocated to both 1304 and 1307 on a timeslot basis according to demand: therefore TRU
1112 is acting as a higher layer cell for both 1304 and 1307.
Conceptually, TRU 1 112 is a higher layer cell for all zones that use that channel frequency.
Note that coverage area 1307 is served by base carrier TRU
1302, thus base carrier TRU 1301 and base carrier TRU 1302 must cooperate to share the higher tier resource 1112. This is simply done by treating TRU 1112 as a high tier cell to 1302 and 1301 i.e. the switch matrix 409 can use existing prior art hierarchical cell structure techniques for call setup, handoff, etc. Note that unlike prior art hierarchical cells, the switch CA 0221~079 1997-09-09 matrix 409 also supports non-contiguous high tier cells (1304 and 1307 are non-adjacent) and could similarly be demand assigned to coverage areas 1304 and 1307 (with the restriction that an in-use timeslot on a specific channel frequency can only be allocated to a locale once).
- As an alternative to the base carrier TRU 1301 informing the switch matrix 409 of the requirement for channel frequency and timeslot service, this can be done by the location information of the RF repeater system i.e. base carrier TRU 1301 can command a mobile to communicate on a specific channel frequency and timeslot, and mobile's allempl~ to communicate will be detected by the local RF repeaters that then communicate channel frequency and timeslot information (as well as locale), to the switch matrix 409. This approach has the advantage of not requiring "special" modifications to TRU 1301.
Figure 14 shows a variant of the wireless loop system of Figure 11. In Figure 11 and all preceding discussions it has been assumed that mobiles such as 1401 can transition between the coverage zones of the distributed antenna arrays 1105, 1106, 1107 and 1108 by classical means (not shown) well known to those of ordinary skill in the art. In many cellular and PCS systems this would mean the mobile 1401 changing its operating carrier frequency as it transitions from one coverage zone to another, and that two base station transceivers are involved. The first base station transceiver would support the mobile in the coverage zone of the initial distributed antenna array and the second base station transceiver would support the mobile in the coverage zone CA 0221~079 1997-09-09 of the second distributed antenna. In Figure 14, the mobile 1401 is supported by one and the same base station transceiver (1112 in the illustrated example) irrespective of it roaming between the coverage zones of two adjacent distributed antenna arrays. In Figure 14, the base station transceiver 1112 is connected to the mobile 1401 via the switch matrix 409 and the initial distributed antenna array 1105, and the mobile 1401 and the base station l,a,~sceiver 1112 communicate with each other using appropriate frequencies/timeslots/codes. When the mobile 1401 transitions to the adjacent coverage zone the switch matrix 409 connects the same base station transceiver 1112 to the corresponding distributed antenna array, for example distributed antenna 1108, albeit with a change in operating frequency/code/timeslot for the base station transceiver 1112. This method of supporting mobiles is inherently more efficient; no longer is a minimum of two base station transceivers necessary to support a roving mobile, but only one.
Because of the increased trunking efficiency and utilization associated with the combination of distributed antenna arrays and switch matrix, a number of uses of the technology are envisaged as described in Figure 15:
- the fiber optic links enable consolidation of BTS key equipments at a master site 1501;
- the w;,eless local loop system can be implemented as a microcell underlay 1502 used in combination with a macrocell overlay 1503;
' CA 0221~079 1997-09-09 - a V~ less local loop system such as 1504 can be used to extend a macrocell such as 1503 in residential districts where high rise towers and buildings are prohibited; and - a wireless local loop system such as 1505 can be used as a macrocell extension in buildings where penetration losses block signals from outside, for example in large shopping centers.
Although the present invention has been described hereinabove by way of a preferred embodiment thereof, this embodiment can be modified at will, within the scope of the appended claims, without departing from the spirit and nature of the subject invention.