GB2374492A

GB2374492A - Bandwidth efficient operation of a wireless local loop

Info

Publication number: GB2374492A
Application number: GB0109240A
Authority: GB
Inventors: Stephen Temple
Original assignee: NTL Group Ltd
Current assignee: NTL Group Ltd
Priority date: 2001-04-12
Filing date: 2001-04-12
Publication date: 2002-10-16
Anticipated expiration: 2021-04-12
Also published as: GB2374492B; GB0109240D0

Abstract

The invention provides a base station for a wireless data communication system, for serving a plurality of system users located in a base station service area. The base station has one or more transmitters for transmitting data to the system users on at least two different frequencies and is configured to transmit data for a first subset of the system users at a first data rate on a first frequency and using a first bandwidth, and to transmit data for a second subset of the system users at a second data rate on a second frequency and using a second bandwidth, the first data rate and first bandwidth being different to second data rate and second bandwidth. Providing a base station transmitting using two different bandwidths to two separate subsets of users allows optimization of the available frequency spectrum. Preferably the first and second frequencies and bandwidths define first and second channels, for example a DOCSIS and a Euro-DOCSIS channel, the channels occupying substantially adjacent parts of wireless spectrum.

Description

COMMUNICATION SYSTEM This invention relates to wireless communications systems, and in particular to systems and methods for bandwidth efficient operation of wireless data transmission systems.

With increasingly heavy use of the Internet, both domestic and commercial users are demonstrating ever increasing demands for greater bandwidth to allow faster access to data and to provide high quality sound and video services at acceptable quality levels.

At present the majority of home Internet connections are made by dialling up a local service provider by telephone, using either a land line connection or a mobile telephone.

In such communication systems the bulk of the cost is in the last few kilometres of "local loop"cable connection to a given subscribers home. By contrast, radio and television sounds and pictures are transmitted over the air to many subscribers simultaneously.

Increasingly, the potentially high bandwidth capability of fibre optic cable and copper cable connections is being exploited to provide fast Internet access for business and domestic subscribers. This is seen as a more appropriate use of data communication pathways since cable connections are thought to be intrinsically capable of providing higher bandwidth services than radio links, which suffer from spectrum congestion and data rate limiting factors such as multi-path fading.

The majority of so-called cable modems operate using a communications protocol known as DOCSIS (Data Over Cable Service Interface Specification), versions 1.0 and 1.1 of which are hereby incorporated by reference. This standard, which is well-known to those skilled in the art, is also known as CableLabs (Trade Mark) Certified Cable Modems project. The radio frequency interface specification is set out in documents SP-RFI-I05-991105 and, for version 1.1, SP-RFIvl. 1-105-000714, which are hereby incorporated by reference. Other relevant documents include cable modem to customer

premises equipment interface specification SP-CMCI-104-000714, cable modem termination system network side interface specification SP-CMTS-NSI-101-960702, cable modem Telco return interface specification SP-CMTRI-IOl-970804, operations support system interface specification SP-OSSIv1. 1-102-000714, and base line privacy

plus interface specification SP-BPI±I05-000714. Further information on the DOCSIS specification can be found at www. cablemodem. com and at cablelabs. com.

The characteristics of cable connections particularly optical fibre data connections, are very different to those of radio data transmission links. Optical fibres provide large bandwidths and low transmission losses and are often used, for example, for longdistance, high-speed telecommunications. Optical fibres are also immune to electromagnetic interference and the multi-path effects encountered in rf transmission links.

The DOCSIS specification defines interface requirements for cable modems for highspeed data distribution over cable television networks. In this specification the term "cable network"is used to cover both all-coax and hybrid-fibre/coax networks.

DOCSIS is widely used in the cable television industry, particularly in the USA, for the provision of high-speed Internet services over a cable television infrastructure. When used in this way it provides an additional Internet Protocol (IP) data path from a cable operator's head end (s) to local subscribers. The specification also defines optional operations support system functions for, inter alia, security, network management, accounting, and configuration and fault management. The specification includes physical, link and network specifications and provides definitions for aspects of the system including features such as rf levels, multiplexing, contention control, and the like.

To provide such an additional data path, an interface device is located at the head end of the cable network. This device has an Internet interface for sending and receiving data to and from the Internet, and a cable interface, coupled to the cable TV distribution system. A downstream output is up-converted to a suitable part of the cable network frequency spectrum and is broadcast to all connected subscribers/customers. An

upstream input receives signals that have been sent by a particular subscriber or customer. At the customer end cable modem customer premises equipment is located at the customers'homes. A cable side of this equipment is connected to the cable TV network by coaxial cable, and a customer interface is provided comprising a standard 10 Base T Ethernet connection for a Personal Computer.

Figure 1 shows a simplified block diagram of a prior art data-over-cable system 100 using DOCSIS equipment. Cable network 102 typically has a tree and branch structure with a single trunk input 103, normally an optical fibre, fanning out to a plurality of branch outputs, coupled to fibre optic and/or coaxial cable links to local subscribers. In this specification"subscriber"has a broad meaning encompassing any user of a data communications system and/or recipient of a data communication service and is not limited to only registered or paying customers or users.

Normally, (although not always), the"input"and the"outputs"are bi-directional. In the DOCSIS specification one frequency band (for example 120 to 850 MHz) is allocated to downstream links from the head end to the subscriber ends whilst a second frequency band (for example below 80 MHz) is allocated to upstream links from subscribers to the head end or hub. Data broadcast from the head end is normally received by all the subscribers, and correspondingly signals may be sent from the subscribers to the head end. Signals sent to the head end simultaneously from two different subscribers may collide.

A subscriber link is coupled to a cable modem 116 located at the subscriber's premises.

Cable modem 116 provides an output to a communications port on a personal computer 118. The DOCSIS-compatible cable modem 116 forwards Internet Protocol traffic, for example using transparent bridging or network-layer forwarding, and may also support other network layer protocols. The link from the cable modem to PC 118 is typically an Ethernet connection (lOBase-T, IEEE 802.3) ; the PC runs standard TCP/IP software.

Fibre optical cable 103 is coupled to physical interface 104 which in turn is coupled to a Cable Modem Termination System (CMTS) 106. The CMTS 24 provides network layer forwarding or transparent bridging for Internet Protocol traffic to a network side

interface (NSI) 108. The NSI 108 typically comprises an ATM (asynchronous transfer mode) network and links to one or more local server (s) 112, remote server (s) 110 and the Internet 114. The servers include a network management server, a billing server.

Other network components, not shown in Figure 1, include one or more central office switches, ISP routers, and frame relays, DHCP (Dynamic Host Configuration Protocol) and TFTP (Trivial File Transfer Protocol) servers, and associated databases. Both cable modem 116 and CMTS 106 function as IP hosts. The system can transparently transfer IP traffic of a variety of types including broadcast and multicast IP Group addressing.

In the DOCSIS specification, broadcast data is encrypted and subscriber-specific data is extracted by a subscriber's cable modem. Upstream bandwidth from a subscriber to the head end is divided into a stream of mini-slots and the CMTS controls access to the slots by the cable modems, determining which mini-slots are subject to collisions (subscribers initially transmit a short"request to send"message). Further information on the DOCSIS specification and its operation can be found at the web sites referenced above.

As already outlined, rf data links suffer from a number of problems including multi-path fading which is caused when a receiver picks up signals from a transmitter which have reached the receiver by travelling over paths of different effective lengths. This causes data bits originally emitted at different times to arrive at the receiver at the same time causing intersymbol interference and notches in the receiver frequency response.

Typically these problems begin to appear at data rates of a few 100K bits per second and above and are particularly apparent at the microwave frequencies (1 GHz and above) which are necessary both to provide the required bandwidth and to avoid conflict with existing spectrum usage allocations. Typical error correction schemes for rf data transmission employ complicated adaptive equalisation, the use of significant redundancy and data interleaving and, in some wireless LAN systems, spread spectrum techniques.

For these reasons, the provision of wireless local loop data services has heretofore focused on providing specific tailor-made solutions involving sophisticated error

correction and techniques for improving spectrum efficiency, that is, traffic carrying capacity for a given bandwidth. Whilst high speed wireless data links are available the equipment required for robust operation is complex and expensive, typically costing f250K for head end equipment and around E2, 000 for subscriber end equipment. By contrast, known cable data transmission systems are relatively simple and cheaptypically subscriber end apparatus costs only a couple of hundred pounds.

Wireless Internet access at an affordable price is highly desirable as it would allow new service providers to offer services without having to rely on using the existing copper or fibre optic cable infrastructure. There is also a need for the improved subscriber mobility and facilitate fast Internet access whilst on the move, which a wireless system could offer. However the cost of this equipment and the difficulties in installing it at domestic premises provide a significant barrier to mass adoption of wireless local loop Internet access schemes.

The above problems with the provision of wireless local loop data services are addressed by an invention described in the applicant's earlier UK patent application, number 0001901. 8 of 27 January 2000, according to which there is provided a wireless data communication system comprising: a DOCSIS-compatible cable modem network system having a data input couplable to the Internet; a radio frequency (rf) transmitter coupled to the cable modem network system and to a transmit antenna; at least one radio frequency (rf) receiver coupled to a receive antenna; and at least one DOCSIScompatible cable modem coupled to the microwave receiver, and having a data output; whereby data from the data input is transmissible to the data output.

In other aspects the earlier invention provides a method of communicating Internet Protocol data over a wireless rf link comprising: encoding the data using a DOCSIScompatible cable modem network system to provide a radio frequency (rf) encoded data output; transmitting the encoded data over a wireless link to a receiver ; receiving the encoded data using the receiver; and decoding the encoded data using a DOCSIScompatible cable modem to provide a decoded data output and a use for DOCSIScompatible cable modem devices in such a method and system.

In a further aspect the earlier invention provides a wireless local loop system designed to provide the same functionality as a cable modem system over a cable TV network in such a way that a cable modem on a customer premises designed to the DOCSIS technical specification for use over a cable TV network can be plugged into the wireless local loop system without modification and successfully provide the same functions.

In a still further aspect the earlier invention links equipment intended to be placed at the head end of a cable TV network (by virtue of its compliance with the DOCSIS technical specification) with equipment on a customers premises that is intended to be connected to the termination of a cable TV network (by virtue of its compliance with the DOCSIS technical specification) by means of a wireless transmission system.

The applicant recognised that the tree and branch structure of a cable network is an environment which has functional similarities to a point to multi-point microwave communication system, in that both systems share requirements for selective data reception and for collision handling for data sent by customers/subscribers to the head end or, in the case of an RF system, to a local base station.

The applicant also conducted a number of experiments and discovered the unexpected result that DOCSIS-compatible cable modem equipment provides acceptable performance levels when used in a wireless local loop system, particularly when operating at relatively high frequencies, such as microwave frequencies where radio wave propagation is relatively directional. This runs counter to earlier technical prejudices and allows a significant advance in the price/performance of wireless local loop systems to be achieved by exploiting existing mass-produced cable modem equipment.

The above-described wireless data communication system need only provide a one-way link from a base station to the subscribers, as a return path can be provided by other means, for example the public switched telephone network (PSTN). However, preferably the system employs transceivers at both the base station and subscriber ends

to provide a bi-directional radio frequency link. This simplifies both lower layer communications such as re-requesting packets with errors, and higher level data communications such as web-telephony and video. The system can be used with RF signals of any frequency but preferably it is used at frequencies above 1 GHz, and more preferably at around 10 GHz-20 GHz although, for greater directionality and bandwidth, frequencies above 20-40 GHz, may be employed.

The above-described wireless system is primarily envisaged for the transmission of Internet data (which includes text, audio and video data), but it can also be used for transmitting other data, for example suitably packaged MPEG data and/or ATM data.

Advantageously DOCSIS forward error correction is enabled for improved robustness.

In a preferred arrangement there is a plurality of local subscribers each with a transceiver and DOCSIS compatible-cable modem, to provide a plurality of bidirectional rf links. To reduce the effects of multi-path it is preferable that the subscribers'antennas are relatively directional, for example with a gain of 3, 6,9, 12 dBi or greater. Advantageously a patch antenna or path antenna array can be used to provide sufficient directionality. Radio frequency digital data transmission systems tend not to degrade linearly but, to a first approximation, either function acceptably or fail to function at all, which facilitates the determination of how well a system for a plurality of subscribers is working.

The present invention relates to this earlier system, although its use is not limited to such systems.

Referring to Figure 2, this shows a conceptual schematic diagram of a wireless local loop data transmission and reception system. A base station 202 comprises a base station transceiver (not shown) coupled to an antenna 204 for transmission and reception of rf signals from and to the base station. The base station is also coupled to a data communications network 214, such as a cable tv network, for providing data services, such as Internet services, to service subscribers. Domestic homes 206a-c each house data communication service subscriber equipment comprising a subscriber

transceiver (not shown) coupled to a respective subscriber equipment transceiver antenna 208a-c. Further base stations which are also coupled to communications network 214, such as base stations 210 and 212 in Figure 2, are provided for service subscribers in other areas.

Figure 3a shows an idealised wireless DOCSIS communications system 300 comprising three base station transceiver radio towers 308, 310 and 312, and three corresponding subscriber service areas 302,304 and 306. Referring again to Figure 2, antenna 204 of base station 202 is located on a tower such as radio tower 308 and subscribers 206a-c are located within a corresponding service area, such as area 302. In Figure 3a, service areas 302,304 and 306 are shown as hexagonal cells but, in practice, these will have irregular and overlapping coverage areas.

In the illustration of Figure 3a subscriber service area 304 is shown as subdivided into three service regions 304a, 304b and 304c, all served by a single radio tower, tower 310.

Other subscriber service areas, such as areas 302 and 306 may be subdivided into more or fewer service regions (or may not be subdivided) depending upon the local geography, the required network capacity, expected traffic, interference, cost and other factors. For example where a high traffic capability is required to serve areas densely populated with subscribers it is preferable to allocate six or more service regions to a subscriber area or cell, as is described in more detail later.

In the example of Figure 3a, radio tower 310 is provided with three separate sets of transceiver antennas (not shown), one for each of the service regions, and each of these is coupled to a separate transceiver. The transceivers, which are normally co-located at a single physical base station location, are in turn each coupled to a respective Cable Modem Termination System (CMTS) and thence to a network site interface (NSI) such as described with reference to Figure 1.

Referring now to Figure 3b, this shows two adjacent service regions 322 and 324 served by a single radio tower 320. As illustrated, there is overlapping coverage of an area

between the two regions. Similar overlapping coverage is found between two adjacent subscriber service areas, such as areas 302 and 304 of Figure 3a.

A downstream transmission is a transmission from a cable head-end or hub to a subscriber or network end user. In a conventional cable tv network, a cable modem will attempt to lock unto the first downstream frequency it finds during its boot process. The number of modems operating on each downstream frequency is limited, to control downstream traffic and thus maintain network performance levels.

In a wireless environment, such as that shown in Figures 3a and 3b, the communications network is subdivided into a plurality of service areas and service regions, which may be termed sectors or cells, and different downstream frequencies are allocated to different sectors, for example to balance the number of cable modems operating on a given downstream frequency. Thus different geographical areas operate using different downstream frequencies. As conceptually illustrated in Figure 3b, customer premises equipments (CPEs) 326 at the subscriber-end are located in region 322 and CPE 328 is located in region 324. A difficulty arises for CPEs 330 in an area of overlapping coverage in ensuring that these modems use their assigned frequencies, but this is addressed in the Applicant's co-pending UK application number 0101721. 9, to which reference can be made.

DOCSIS is a North American specification and there is an equivalent European specification generally referred to as EuroDOCSIS, to which reference may also be made. Broadly speaking, EuroDOCSIS corresponds to North American DOCSIS, but with an altered frequency plan to take account of the use of 8 MHz PAL/SECAM analogue television signals rather than the narrower bandwidth 6 MHz NTSC analogue tv system used in North America. In particular EuroDOCSIS uses 7/8 MHz channels (8 MHz channels are used for data communication) whereas North American DOCSIS uses 6 MHz channels. With the 64 QAM (quadrature amplitude modulation) modulation employed in cable modems (North American) DOCSIS provides a gross data rate from cable head end to customer of 27 Mbps using the 6 MHz channel whilst EuroDOCSIS provides 38Mbps using the 8 MHz channel.

There are North American DOCSIS cable modem systems that are operational in Europe and these locate the 6 MHz channel needed within the 8 MHz channel provided on the European cable TV network. In other words they do not optimally use the bandwidth available. This is relatively unimportant in conventional cable networks as a separate communication path is provided to each subscriber. However, it becomes important where the link to a subscriber's home is via a wireless local loop so that, in effect, groups of subscribers must share a communication pathway. Wireless bandwidth is expensive for system service providers and efficient use of spectrum allocations and ensuring high spectral occupancy are significant commercial problems.

The above-described wireless high speed access modem ("Wham") is designed to provide a clean interface between a standard DOCSIS or EuroDOCSIS system and a microwave transmitter/receiver requiring no modification to the DOCSIS (or EuroDOCSIS) system and allowing use of a conventional DOCSIS (or EuroDOCSIS) cable modem at the customer premises end.

In Europe the European Technical Standards Institute (ETSI) defines frequency bands for spectrum allocation purposes. These bands are therefore common to countries adopting these ETSI standards, which include the EU countries, the definition helping to avoid cross-border interference between licensed users. Other countries use similar principles but adapt different standards. The relevant ETSI standard defining channels for the 10 GHz microwave band is ETSI EN 301 081 (DEN/TM-04046,"Transmission and multiplexing ; FDMA point to multipoint Digital Radio Relay Systems (DRRS) in the band 3 to 11 GHz") which defines 14 MHz channels or bands for allocation to wireless system service providers. Reference may also be made to EN 301 213-2.

However, when operating a DOCSIS-based wireless local loop the most efficient use of the radio frequency spectrum, and the most economically provided service, would be where the microwave channel bandwidth was an exact multiple of either 6 MHz or 8 MHz.

A practical implantation of the above-described wireless DOCSIS system will usually segment the antenna array at the base station as shown, for example, in Figure 3a.

Adjacent radio beams from the antenna array are then allocated different radio frequency channels, either 6 MHz or 8 MHz channels depending upon whether the cable modem systems is configured according to the DOCSIS or EuroDOCSIS standard, to provide spatial diversity and spectrum re-use. However, this does not provide the best use of the available rf spectrum allocation, particularly because of the tendency for this rf spectrum to be partitioned into channels with a spacing which, in general, does not match that of either of the DOCSIS standards. The present invention therefore seeks to provide systems and methods for improved spectral efficiency and bandwidth allocation.

According to the present invention, there is therefore provided a base station for a wireless data communication system, for serving a plurality of system users located in a base station service area; the base station having one or more transmitters for transmitting data to the system users on at least two different frequencies; wherein the base station is configured to transmit data for a first subset of the system users at a first data rate on a first frequency and using a first bandwidth, and is configured to transmit data for a second subset of the system users at a second data rate on a second frequency and using a second bandwidth, the first data rate and first bandwidth being different to second data rate and second bandwidth.

The base station transmits traffic data for use by the system users on two different frequencies, using two different bandwidths, for example, the 6 MHz bandwidth of DOCSIS and the 8 MHz bandwidth of EuroDOCSIS. Generally the first and second frequencies will be different to avoid mutual interference.

Dividing the system users into two separate subsets and using data transmissions of different bandwidths for each subset allows a predetermined frequency band, such as a band defined by ETSI, to be more efficiently utilized for carrying data traffic. As explained above, for convenience licensing authorities divide the spectrum into a plurality of predetermined frequency bands defined by upper and lower frequency limits and by appropriately selecting the first and second bandwidths transmissions to the

system users can be arranged to substantially fill the space between these predetermined limits (bearing in mind the need for guard bands and the like). The invention thus helps optimize frequency spectrum usage by a wireless data communications system.

In a preferred embodiment the first frequency and bandwidth define a first channel and the second frequency and bandwidth define a second channel substantially adjacent to the first in the frequency domain. Abutting the channels in this way (apart from any necessary guard bands) allows a licenced frequency band to be substantially fully occupied. Thus, in a particularly preferred embodiment, the first bandwidth is the 6 MHz bandwidth of the (US) DOCSIS specification and the second bandwidth is the 8 MHz bandwidth of the EuroDOCSIS specification which, together, total 14 MHz, which corresponds to the frequency band or channel spacing used by ETSI in the 10 GHz region of the microwave spectrum.

In one embodiment the first and second subsets of users are located in respective first and second regions of the base station's coverage and these regions mutually separate one another-in other words, the first regions are interspersed between the second regions and vice versa. In a preferred version of this embodiment the first regions are in a first set of angular directions from the base station and the second regions are in a second set of angular directions from the base station, and the regions are angularly interleaved with one another.

The base station may also transmit on third and fourth frequencies using, respectively, the first and second bandwidths, thus defining third and fourth wireless channels.

Preferably these third and fourth wireless channels are also substantially adjacent one another in the wireless spectrum, the first and second wireless channels defining a first frequency band and the third and fourth channels defining a second frequency band.

The first and second frequency bands may be two permitted frequency bands as defined by a spectrum licensing authority.

In an embodiment different to that described above (where the first and second regions are mutually spatially separated from one another) the first and second regions may

overlap or be substantially coincident, being separated in the frequency rather than the spatial domain. In this embodiment the first frequency band may be reused by the base station by separating regions of coverage operating within the first frequency band by other regions operating within the second frequency band.

Where, say, the first bandwidth is narrower than the second bandwidth so that the first data rate is less than the second data rate, the base station is preferably configured such that regions receiving transmissions at the second data rate using the second bandwidth are those having a relatively greater number or density of system users. This optimizes use of the bandwidth and data rates available insofar as users are concerned. Generally this may be accomplished by directing transmissions at the second frequency broadly towards areas with greater numbers or densities of users, although it will be recognized that the direction need not be exact.

In some embodiments there will be further constraints on the directions of transmission or regions defined for reception at the first and second frequencies, for example, dictated by a desire not to position regions receiving at the same frequency adjacent one another.

Thus where, for example, in the arrangement described above the transmissions at the first and second frequencies are spatially interleaved it may only be possible to select one or a few directions having higher numbers or densities of users for reception at the higher data rate or rates. In this case one approach is to select a region having the highest number or density of users and choose this for reception at the second frequency (higher data rate), afterwards adding further regions for reception at the first and second frequencies to fit with this initial choice.

The invention also contemplates a wireless data communications system including such a base station. In a preferred embodiment this system transmits from the base station using both (US) DOCSIS and EuroDOCSIS bandwidths and, preferably, one or more of the users is provided with a cable modem capable of auto-sensing whether it is receiving data according to the (US) DOCSIS or EuroDOCSIS standard. More preferably all the users in a region, and most preferably all the users in the area served by the base station,

have such an auto-sensing modem, to avoid the need to modify customer premises equipment should the base station configuration be changed.

In another aspect the invention provides a wireless data communications system comprising: a DOCSIS-compatible cable modem network system having a data input couplable to the Internet; two radio frequency (rf) transmitters each coupled to the cable modem network system and to a transmit antenna, a first rf transmitter having a bandwidth of approximately 6 MHz and a DOCSIS-based interface to the cable modem network system, and a second rf transmitter having a bandwidth of approximately 8 MHz and a EuroDOCSIS-based interface to the cable modem network system; at least one radio frequency (rf) receiver coupled to a receive antenna; and at least one DOCSIS or EuroDOCSIS-compatible cable modem coupled to the microwave receiver, and having a data output; whereby data from the data input is transmissible to the data output.

According to a further aspect of the invention, there is provided a method of configuring a wireless data communication system, the wireless data communication system including a base station and a plurality of wireless receivers for the plurality of system users in the base station service area, wherein the first subset of system users is distributed in at least one first region and the second subset of system users is distributed in at least one second region, wherein the base station is configured to transmit on said first frequency to the at least one first region and to transmit on said second frequency to the at least one second region, and wherein said second data rate is greater than said first data rate; the method comprising: identifying a region of the service area having a relatively greater requirement for data traffic than another region of the service area; and configuring the base station such that one or more of the second regions overlaps to the identified region.

This method assists in configuring the base station for optimal use of the available bandwidth for serving users within the base station's coverage area.

These and other aspects of the present invention will now be further described, by way of example only, with reference to the accompanying figures in which: Figure 1 shows a simplified block diagram of a known data-over-cable system using DOCSIS equipment; Figure 2 shows a wireless local loop data communication system; Figures 3a and 3b show service areas and regions for a radio communications network; Figure 4 shows an outline schematic diagram of a DOCSIS-based data transmission system incorporating a wireless local loop; Figure 5 shows a schematic diagram of an rf transceiver for the system of Figure 4; Figure 6 shows base station equipment for a DOCSIS-based wireless communications system; Figures 7a to c show examples of bandwidth allocation within regions of a base station service area; and Figure 8 shows an example of bandwidth allocation for a plurality of service areas covered by a plurality of base stations.

Referring now to Figure 4, this shows an outline schematic diagram of equipment 400 located at a base station 202 and at subscriber premises 206 in a wireless local loop system employing DOCSIS standard cable modem apparatus.

The subscriber premises equipment 400 comprises a microwave antenna 408 coupled to a microwave transceiver 406; the equipment may also include a preamplifier and/or low-noise block downconverter (LNB) (not shown) in some applications. The equipment also comprises a conventional DOCSIS cable modem 116 and a home PC

118, as shown in Figure 1. In one embodiment microwave transceiver 406 interfaces to the DOCSIS cable modem 116 by means of a simple coaxial cable connection.

The subscriber end equipment from transceiver 406 onwards towards the customer corresponds to that used in a conventional cable network system. Cable modem 116 provides a conventional Cat 5 connection for use with a hub, switch or router, or other Internet protocol hardware or, as illustrated, personal computer 118. Other types of customer premises equipment, for example an Internet enabled television or set top box, can also be used. In a typical installation the interface to PC 118 comprises a Cat 5 cable connection to an Ethernet NIC (Network Interface Card).

In some embodiments antenna 408 is a simple printed patch antenna, but a patch array or yagi may be used where greater directionality is desired. Antenna 408 is preferably selected taking into account physical size, bandwidth and filter requirements. If necessary to reduce the bit error rate, additional filtering or equalisation can be included in microwave transceiver 406. Microwave transceiver 406 may also include an up converter and/or power amplifier (not shown) for return transmissions from the subscriber to the base station at microwave frequencies.

At base station 202 a base station microwave transceiver 402 is coupled to a base station antenna 404. As with transceiver 406 and antenna 408, up and down converters, preand power amplifiers, and filters and equalisation (not shown) may also be included. A less directional or omnidirectional antenna or antennas is (are) preferred for base station 202 because there is usually a need to transmit to subscribers located over a range of directions. Antenna 404 may therefore be, for example, a dipole antenna. The transmission power of the base station is generally higher than that of a subscriber's transceiver, because of the greater coverage required, and also because of the different frequency and data rates of the down and up links.

Microwave transceiver 402 interfaces to the CMTS 106 of a conventional cable network system of the type illustrated in Figure 1. For simplicity details of the cable network system are not shown in Figure 4 but the skilled person will understand that the system

will include a DOCSIS-compatible Cable Modem Termination System (CMTS) 106, coupled to a network side interface 108 comprising an ATM core and to the Internet 114, as well as other elements shown in Figure 1. The cable network system will also include a server complex including a DHCP server to verify each subscriber's MAC address, a caching server, and other local and remote servers coupled to the ATM core.

CMTS 106 is provided with an appropriate physical interface to microwave transceiver 402, which will in general separate downstream and upstream data. The network side of CMTS 106 will generally be coupled to a switch. The link between transceiver 402 and CMTS 106 may comprise a coaxial cable or a fibre optic cable; the link from CMTS 106 to the ATM core normally comprises a fibre optic cable and may also include an rf link such as a microwave link.

The single-cable interface to microwave transceiver 402, carries rf frequency multiplexed data. At an appropriate electrical interface, that is at this or another physical interface where such a single cable interface to the cable tv system exists, microwave transceiver 402 can be coupled to the cable modem network system with substantially no modification to the network system. Thus, in effect, the base station and subscriber rf transceiver equipment replaces the wired cable network 10 shown in Figure 1.

Figure 5 shows subscriber end equipment comprising an rf transceiver 500 suitable for use with the transmission system of Figure 4. The transceiver comprises a transmit/receive antenna 502 (although separate antennas could be employed) coupled to a duplexer 504 which provides signals received on antenna 502 to a received signal output and which provides signals received at a transmit signal input to antenna 502.

The transmit signal input of duplexer 504 is coupled to a transmitter 512 which in turn is coupled to an rf interface of a cable modem 514. The received signal output of duplexer 504 is coupled to an attenuator 506 to attenuate the received signal level, and an output of attenuator 506 is coupled to downconverter 508, which in turn is coupled to a receiver 510. Receiver 510 is also coupled to the rf interface of cable modem 514.

Attenuator 506 is preferably located prior to any sensitive input circuitry in the received

signal path. A data interface of cable modem 514 is coupled to a home PC, as shown in Figure 4, or to a switch, router or some other network device.

As used herein,"receiver"and"transmitter"refer to apparatus providing an rf interface for cable modem 414 and they need not provide an interface for baseband data.

In one preferred embodiment the rf signals received by and transmitted from antenna 502 have a frequency of approximately 10 GHz, although in other embodiments higher (or lower) frequencies may be employed. Where increased receive data rates are desired higher frequencies are used, such as, approximately 28 GHz or 40 GHz. Downconverter 508 downconverts the received signal to a lower frequency, normally around 1 GHz, for input to receiver 510.

A single co-axial cable couples cable modem 514 to receiver 510 and transmitter 512.

This cable carries rf frequency domain multiplexed signals in a frequency range of 0- 750 MHz, that is, different frequencies or frequency bands are used for upstream and downstream channels to and from transceiver 500. The signals to and from the cable modem and hence the signal input to the transmitter and signal output from the receiver comprise rf signals rather than baseband signals. Thus the receiver effectively operates as a downconverter and the transmitter as an upconverter and power amplifier. In some embodiments the"transmitter"and"receiver"may be combined as a transceiver.

The cable modem 514 converts rf signals on the co-axial cable linking it to receiver 510 and transmitter 512 to Ethernet (physical layer) signals on unshielded twisted pair (UTP) data output carrying, at the transport layer, Internet protocol (IP) data.

Cable modem 514 operates as defined in the DOCSIS standard. According to this standard, the cable modem adjusts the transmit power according to the received signal level, increasing the output power when the received input signal is at a lower level, with the aim of maintaining an approximate 0 dB signal level at physical interface 104 of Figure I. As shown in Figure 5, attenuator 506 is located in the received signal path but not in the transmitted signal path. The effect of this is to ensure that cable modem

514 provides a high level transmit output signal, which is desirable for a wireless data transmission system as, generally speaking, such systems are more prone to unpredictable signal losses, particularly in the return path to the base station transceiver, as compared with wired cable systems.

Referring now to Figure 6, this shows base station equipment 600 for use with a DOCSIS-based wireless local loop communications system, such as that shown conceptually in Figure 4.

A base station transceiver 602 is coupled to two base station antennas, antenna 604 and antenna 606 each of which serves a different region associated with the base station, such as regions 322 and 324 of Figure 3b. Base station transceiver 602 comprises a pair of transceivers (not individually shown) each transmitting at a different downstream frequency, and each coupled to a respective antenna 604 and 606. Each separate transceiver is coupled to a corresponding card of a universal broad band router (UBR) 616. Antenna 604 and its respective transceiver, providing coverage in a first sector, is coupled to Card A 618 of universal broad band router of 616 whilst antenna 606, and its respective transceiver covering a second sector, is coupled to Card B 620 of universal broad band router (UBR) 616.

Universal broad band router 616 is a commercially available device with an Ethernet interface and a plurality of radio frequency interfaces. Such devices are available from, for example, Cisco. As shown UBR 616 comprises one or more"cards", each card having a separate Ethernet MAC address. Each card provides a single downstream (DS) rf output and a plurality of upstream (US) rf inputs. The rf operating frequency of the upstream and downstream rf ports are software configurable and, in a conventional cable tv system, all the upstream ports are set for operation at the same frequency since the upstream channels are physically separated on different cable links. However, in the present wireless DOCSIS system each upstream is set for operation at a different frequency, for example, 19 MHz, 21 MHz, 23 MHz, 25 MHz and so on. The downstream channel is configured for operation at, in one embodiment, approximately

40 MHz. The upstream and downstream frequencies may be split to allow the base station transceiver to serve different sectors as the number of subscribers grows.

Since the wireless local loop transmission system will generally operate at a different frequency to the frequencies of the upstream and downstream ports of the UBR 616, the outputs from and inputs to the UBR 616 must be up/downconverted for base station transceiver 602. The HF frequencies at which UBR 616 operates are generally not suitable for wireless local loop data transmission and the operational frequencies will generally be selected taking into account applicable radio communications licensing regulations.

In the embodiment of Figure 6, downstream outputs from cards 618 and 620 of UBR 616 are up-converted by up-converters 610 and 614 respectively, and rf outputs from base station transceiver 602 are down-converted by down-converters 608 and 612 for cards 618 and 620 respectively. Down-converters 610 and 612 also provide a"splitter" function, that is, they divide the downconverted output signal into a number of copies, each of which is presented to an upstream port of UBR 616. The splitting function merely duplicates the rf signal output of the down-converter, and provides some additional buffering and impedance matching.

In one embodiment in one area, base station transceiver 602 transmits downstream to two adjacent regions of coverage using two channels at approximately 10.5 GHz, each downstream channel having a bandwidth either of approximately 6 MHz or of approximately 8 MHz. Reception takes place at approximately 10.2 GHz. In other areas and regions other frequencies are used, frequency planning and re-use generally taking into account cell size and shape, local geography, expected numbers of subscribes and the like.

In Figure 6 UBR 616 operates as a cable modem termination system (CMTS) similarly to CMTS 106 of Figure I. It is, however, not essential to use a UBR as the CMTS.

Other elements of a DOCSIS-based system, such as operations support systems and security servers are not shown in this figure.

Router 616 is coupled to 10/100 Base T Ethernet network 622, to which are also coupled DHCP server 624, TFTP server 628 and time of day server 632. DHCP server 624 comprises DHCP code storage 624a for providing DHCP functions. These are well known to the skilled person, defined in, for example, RFC 2131, and described more specifically below. TFTP server 628 comprises TFTP code storage 628a, for providing TFTP functions. These are also well known to those skilled in the art, are defined in RFC-1350, and described in more detail below in the context of this embodiment. Time of day server 632 comprises time of day code storage 632a for providing time of day functions and values for use by the system.

The DHCP server 624 is coupled to DHCP database 626 which stores IP configuration data, and network scopes and policies. TFTP server 628 is coupled to TFTP database 630 which stores modem configuration file data and, optionally, versions of cable modem firmware for updating cable modem operating systems, and other files accessible via Ethernet 622. The data stored in databases 626 and 630 may be provided on a removal storage device 640, such as a CD-ROM or removable hard disk.

As is well known to those skilled in the art, servers 624,628, and 632 may reside on separate machines or (preferably), on a single physical computer. Physically, servers 624,628, and 632 may comprise Windows NT or UNIX machines running commercial software such as Cisco"Network Registrar"for the DHCP server and a time server which uses the NTP (network time protocol), such as Tardis.

Also coupled to Ethernet 622 is a default gateway to a core IP network 636, such as an STM-1/16/64 network (each STM channel comprising one 155 Mbps asynchronous transfer mode data channel). In the embodiment illustrated the default gateway comprises a router 634. Core network 636 is coupled to Internet 638, such as the World Wide Web, by an Internet gateway (not shown).

In the embodiment of Figure 6 UBR 616, servers 624,628, and 630 and router 634 are all collocated at a base station and coupled by a local area network (LAN). However, in

other embodiments one or more of servers 624,628 and 632 may be located remotely from the base station, for example at a metropolitan or regional network node and coupled to router 616 over a backhaul network segment.

Referring now to Figure 7a, this shows a first example of bandwidth allocation in an area 700 covered by a base station transmitter 702. In the idealized example of Figure 7a area 700 is approximated as a hexagon but, in general, an area or cell covered by a base station will have a shape dependent upon local geography, the number of subscribers, and the like. Base station service area 700 is subdivided into six regions 704a to 704f, in this idealized example located at 600 intervals around base station transmitter 702. Typically each of these regions will be served by a separate base station antenna, in the illustrated example each antenna having a beam width of approximately 60 . At the base station each antenna is driven by separate transmitter (or transceiver) circuitry coupled via a dedicated CMTS to a backhaul link, for example along the general lines illustrated in Figure 6.

Regions 704a, 704c and 704e are served by antenna-transceiver systems coupled to a (North American) DOCSIS-standard CMTS having a 6 MHz bandwidth, whilst regions 704b, 704 and 704f are served by antenna-transceiver systems coupled to EuroDOCSISstandard CMTSs. The base station antenna array is arranged such that the EuroDOCSIS beams are aligned on angular bearings having the greatest number of registered subscribers. Preferably the subscribers are provided with cable modems that are capable of working using either DOCSIS or Euro-DOCSIS standards. Suitable cable modems are available from companies such as 3COM, Motorola and Cisco (registered trademarks); a more comprehensive list of suppliers can be found at www. cablemedia. com/certification/. html. Preferably the cable modems are capable of automatically sensing whether they are connected to a DOCSIS or Euro-DOCSIS service.

In an embodiment of the system in which the wireless local loop operates in the 10 GHz microwave band (X-band) regions 704a, c and e use a first frequency such as 10.003 GHz, and regions 704b, d and fuse a second frequency, such as 10. 010 GHz,

adjacent beams thus using alternate channels for DOCSIS and Euro-DOCSIS. The total bandwidth occupied by transmissions within the cell or service area is therefore 14 MHz (10.000 GHz to 10.014 GHz) which thus provides full occupancy of a single 14 MHz band as used by ETSI when defining frequencies in the 10 GHz region for licensing within Europe.

Thus by mixing the transmission bandwidths used for transmissions from a single base station location, more effective use can be made of available bandwidth within the microwave channel. The use (US) DOCSIS alone would result in underfilling of a frequency band since only 12 MHz of the available 14 MHz would be employed. The use of Euro-DOCSIS alone would require a licence to operate in two microwave bands since 16 MHz of total spectrum would be required. However, by combining both DOCSIS and Euro-DOCSIS transmissions use of the available spectrum is optimized.

The traffic capacity of Euro-DOCSIS is approximately 30% higher than that of DOCSIS, this being the approximate ratio of the bandwidths. Where the traffic is uniform in all directions the combination of 6 MHz and 8 MHz bandwidths therefore offers an improvement in capacity of approximately 15% over the use of only 6 MHz DOCSIS channels within the 14 MHz channel plan defined for use in the 10 GHz band.

In practice an improvement in the perceived level of customer service is also achieved as the number of customers along different angular directions from the base station is rarely uniform. Thus by pointing the Euro-DOCSIS transmissions in directions where there are greater numbers of customers it is also possible to improve the system load characteristics.

In the bandwidth allocation plan of Figure 7a as described above, regions 704a, c and e and regions 704b, d and f operate on different frequency channels within a single 14 MHz band. In some service areas, however, there may be insufficient isolation between regions operating in the same channel, such as regions 704a, c and e, and in this case other forms of diversity such as polarization diversity may be employed to increase the mutual channel isolation. Alternatively, regions 704a and b may utilize a first

14 MHz frequency band, regions 704c and d may utilize a second 14 MHz frequency band and regions 704e and f may utilize a third 14 MHz frequency band. Where this plan is adopted the base station cell may be configured more along the lines illustrated in Figure 7b in which, in effect, there is overlapping coverage for regions 704a and b, 704c and d and 704e and f. The overlap may be partial or complete.

Thus, referring to Figure 7b, a base station service area 710 has a central base station 712 and three service regions 714a, b and c each served by both DOCSIS and Euro-DOCSIS transmissions, but operating in different 14 MHz microwave frequency bands. An extension of this principle is shown in Figure 7c in which a base station 722 provides coverage for an area 720 divided into six segments or regions 724a to f in each of which transmissions within a single 14 MHz band to some extent overlap. It will be appreciated, however, that in this arrangement DOCSIS and Euro-DOCSIS transmissions within a region 724 will nevertheless be on different frequencies. In the example of Figure 7c separate 14 MHz bands may be used for each region 724.

Alternatively regions may be assigned to alternating bands, for example regions 724a, c and e to a first 14 MHz band and regions 724b, d and f to a second 14 MHz band, or some other frequency planning arrangement may be employed.

Referring now to Figure 8, this illustrates a wireless communications network 800 including a plurality of base stations and associated service areas such as service area 700 of Figure 7a. The idealized network layout 800 of Figure 8 shows that the service areas 700 of Figure 7a may be tessellated without transmission frequency and bandwidth conflicts at service area or cell boundaries.

No doubt many other effective alternatives within the spirit and scope of the present invention will occur to those skilled in the art, and it should be understood that the invention is not limited to the described embodiments.

Claims

CLAIMS: 1. A base station for a wireless data communication system, for serving a plurality of system users located in a base station service area; the base station having one or more transmitters for transmitting data to the system users on at least two different frequencies; wherein the base station is configured to transmit data for a first subset of the system users at a first data rate on a first frequency and using a first bandwidth, and is configured to transmit data for a second subset of the system users at a second data rate on a second frequency and using a second bandwidth, the first data rate and first bandwidth being different to second data rate and second bandwidth.
2. A base station as claimed in claim 1, wherein the first frequency and first bandwidth define a first wireless channel and the second frequency and second bandwidth define a second wireless channel, and wherein the first and second wireless channels occupy substantially adjacent parts of wireless spectrum.
3. A base station as claimed in claim 2, wherein the first subset of system users is distributed in a plurality of first regions and the second subset of system users is distributed in a plurality of second regions, wherein the base station is configured to transmit on said first frequency to the plurality of first regions and to transmit on said second frequency to the plurality of second regions, and wherein said first and second regions mutually spatially separate one another.
4. A base station as claimed in claim 2 or 3, wherein the base station is configured to transmit data at the first data rate to a third subset of the system users on a third frequency using the first bandwidth, and is configured to transmit data at the second data rate to a fourth subset of the system users on a fourth frequency using the second bandwidth, wherein the third frequency and first bandwidth define a third wireless channel and the fourth frequency and second bandwidth define a fourth wireless channel, the third and fourth wireless channels occupying substantially adjacent parts of the wireless spectrum.

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5. A base station as claimed in claim 2, wherein the base station is configured to transmit data at the first data rate to a third subset of the system users on a third frequency using the first bandwidth, and is configured to transmit data at the second data rate to a fourth subset of the system users on a fourth frequency using the second bandwidth, wherein the third frequency and first bandwidth define a third wireless channel and the fourth frequency and second bandwidth define a fourth wireless channel, the third and fourth wireless channels occupying substantially adjacent parts of the wireless spectrum; wherein the first, second, third and fourth subsets of system users are located in respective first, second, third and fourth regions of the service area; wherein the base station is configured to direct transmissions for the first, second, third and fourth subsets of users to the respective first, second, third and fourth regions; and wherein the first and second regions substantially overlap and the third and fourth regions substantially overlap.
6. A base station as claimed in claim 5, wherein the first subset of system users is distributed in a plurality of first regions and the second subset of system users is distributed in a plurality of second regions, and wherein an overlapping pair of said first and second regions is spatially separated from another overlapping pair of said first and second regions by an overlapping pair of said third and fourth regions.
7. A base station as claimed in any one of claims 1 to 6 for coupling to a DOCSISbased cable modem network system, wherein the first bandwidth is substantially as defined in US DOCSIS and wherein the second bandwidth is substantially as defined in EuroDOCSIS.
8. A wireless data communication system including a base station as claimed in claim 7, a plurality of wireless receivers for the plurality of system users in the base station service area, and a corresponding plurality of DOCSIS-type cable modems each coupled to a said wireless receiver; and wherein at least some of the cable modems are capable of automatically determining whether US DOCSIS or EuroDOCSIS signals are being received and of decoding both such signals.

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9. A wireless data communication system including a base station as claimed in any one of claims 1 to 7 and a plurality of wireless receivers for the plurality of system users in the base station service area, wherein the first subset of system users is distributed in at least one first region and the second subset of system users is distributed in at least one second region, wherein the base station is configured to transmit on said first frequency to the at least one first region and to transmit on said second frequency to the at least one second region, wherein said second data rate is greater than said first data rate, and wherein the number of system users in a said second region is greater than the number of users in any said first region served by the base station.
10. A wireless data communication system comprising: a DOCSIS-compatible cable modem network system having a data input couplable to the Internet ; two radio frequency (rf) transmitters each coupled to the cable modem network system and to a transmit antenna, a first rf transmitter having a bandwidth of approximately 6 MHz and a DOCSIS-based interface to the cable modem network system, and a second rf transmitter having a bandwidth of approximately 8 MHz and a EuroDOCSIS-based interface to the cable modem network system; at least one radio frequency (rf) receiver coupled to a receive antenna; and at least one DOCSIS or EuroDOCSIS-compatible cable modem coupled to the microwave receiver, and having a data output; whereby data from the data input is transmissible to the data output.
11. A method of configuring a wireless data communication system, the wireless data communication system including a base station as claimed in any one of claims 1 to 7 and a plurality of wireless receivers for the plurality of system users in the base station service area, wherein the first subset of system users is distributed in at least one first region and the second subset of system users is distributed in at least one second region, wherein the base station is configured to transmit on said first frequency to the at least one first region and to transmit on said second frequency to the at least one second

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region, and wherein said second data rate is greater than said first data rate; the method comprising: identifying a region of the service area having a relatively greater requirement for data traffic than another region of the service area; and configuring the base station such that one or more of the second regions overlaps to the identified region.
12. A base station, data communication system, or method substantially as hereinbefore described with reference to Figures 7a, 7b, 7c and/or 8.