WO2000049739A2

WO2000049739A2 - Method and apparatus for multiplexing multiple gsm control channels to a single carrier

Info

Publication number: WO2000049739A2
Application number: PCT/IB2000/000316
Authority: WO
Inventors: Kari Jyrkka; Antti Lappetelainen; Pekka Mottonen
Original assignee: Nokia Mobile Phones Limited
Priority date: 1999-02-19
Filing date: 2000-02-15
Publication date: 2000-08-24
Also published as: WO2000049739A3; AU2936000A; EP1153487A2

Abstract

A method is disclosed for operating a wireless telecommunications system. The method has a first step of (A) synchronously multiplexing a downlink communication frequency between transmissions of a plurality of base stations such that each base station transmits continuously for a plurality of consecutive time slot periods; and a second step of (B) receiving the transmission from at least one of the plurality of base stations with a mobile station, and transmitting an uplink transmission to one of the base stations from the mobile station during a time when the base station is not transmitting. The downlink transmission from each of the plurality of base stations includes a Broadcast Control Channel (BCCH) signal. The method includes a further step of multiplexing random access uplink transmissions to the plurality of base stations so as to reduce latency. The step (A) of synchronously multiplexing preferably includes a step of inserting a guardtime period between transmissions of different ones of the plurality of base stations.

Description

METHOD AND APPARATUS FOR MULTIPLEXING MULTIPLE GSM CONTROL CHANNELS TO A SINGLE CARRIER

CLAIM OF PRIORITY FROM A COPENDING PROVISIONAL PATENT APPLICATION:

Priority is herewith claimed under 35 U.S.C. §119 (e) from copending Provisional Patent Application 60/120,829, filed February 19, 1999. The disclosure of this Provisional Patent Application is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION:

This invention relates generally to radiotelephones and, in particular, to radiotelephones or mobile stations such as those capable of operation with a cellular network.

BACKGROUND OF THE INVENTION:

One problem that has arisen in the implementation of modern, high speed wireless telecommunications systems is how to integrate the 200 kHz GSM (Global System for Mobile communications) -like carriers into current TDMA systems, such as an IS-136 TDMA system, in order to achieve higher data rates.

One readily apparent solution to this problem would be to simply adopt the EGPRS (8-PSK modulation + GPRS packet channels) from the GSM/ETSI specification. This solution would be attractive, since it could use the significant amount of specification work which has already been done for the GSM 200 kHz carrier.

However, wireless telecommunications system operators would prefer to make the initial 200 kHz deployment using a narrow bandwidth (1 MHz) , while the currently deployed GSM systems require about 2.5 MHz bandwidth. This wider bandwidth is required because each cell in a GSM system must transmit a high power, continuous Broadcast Control Channel (BCCH) signal. The mobile stations use the BCCH signal for synchronization and neighbor cell monitoring. In addition, all of the network parameters and paging messages are received from the BCCH carrier.

Reference can be had to a publication entitled "The GSM System for Mobile Communications", by Michel Mouly and Marie-Bernadette Pautet (1992) for an overall description of the GSM system, the conventional GSM 26 multiframe and 51 multiframe signalling structure (see Fig. 4.15 of Mouly et al . and also Fig. 3 herein), as well as a thorough discussion of the BCCH (see, for example, pages 194, 210 and 440-446) .

It can be appreciated that the interference from continuously transmitting BCCH carriers must be somehow reduced, otherwise the introduction of a 200 kHz network with a 1 MHz bandwidth will not be technically feasible.

The continuous BCCH transmission has been recognized as a problem for some time. The continuous BCCH carrier in the GSM network was originally specified for use in Europe when there was no shortage of available bandwidth. Now, however, the proposed narrowband deployment of the 200 kHz carrier into other TDMA systems, such as the U.S. IS-136 system and the GMS450 band, has forced system designers to face the continuous BCCH problem.

The GSM BCCH carrier contains one timeslot for transmitting the synchronization, broadcast and paging information, while the remaining seven timeslots of the frame are used for traffic. The seven timeslots are always transmitted with full power, even if there is no traffic in these slots. The constant, full BCCH transmitted power of the BCCH carrier is maintained in order to support mobile station cell selection and re-selection measurements, as a mobile station can make neighbor cell measurements whenever it wishes to, and it will always obtain a valid estimate of the received signal level from that particular BCCH frequency.

Previously proposed techniques to decrease the interference due to the continuous, full power GSM BCCH transmission are as follows.

(A) In a first technique one transmits only timeslot 0 with full power, and then the base station uses discontinuous transmission and downlink power control on timeslots 1-7.

(B) In a second technique one multiplexes 4-6 cells so as to transmit their BCCH timeslot using a shared BCCH frequency. For example, six base stations would transmit their BCCH bursts at the same frequency, but at different times. Up to six cells can be multiplexed in this manner, as there must be guard time between each cell transmission to guarantee that they do not overlap at a receiving mobile station.

However, neighbor cell measurements are difficult to make when using either of these proposed techniques. Furthermore, mobile station synchronization and receiver AGC functions become problematic, as a single base station transmits only one burst during the TDMA frame. As such, a mobile station attempting to synchronize to a particular base station has only the one burst per frame to work with.

OBJECTS AND ADVANTAGES OF THE INVENTION:

It is thus a first object and advantage of this invention to provide an improved method for solving the GSM BCCH problem.

It is another object and advantage of this invention to provide a technique to deploy 200 kHz channels using a significantly narrower bandwidth that the bandwidth currently specified for use in GSM systems.

It is a further object and advantage of this invention to provide a technique to deploy 200 kHz channels using a 1 MHz bandwidth, as opposed to the 2.5 MHz bandwidth currently specified for use in GSM systems.

SUMMARY OF THE INVENTION

The foregoing and other problems are overcome and the objects and advantages are realized by methods and apparatus in accordance with embodiments of this invention.

One important aspect of this invention is that a plurality of base stations transmit/receive control and synchronization information on a common, shared frequency or carrier. In particular, a plurality of base stations each transmits its BCCH data on the common, shared frequency. This is done primarily because the synchronization information, broadcast information and paging information are all a type of data which must be transmitted with high power in order to reach the cell edge . In accordance with this invention the system places all of these high power, interference-generating signals in at least one common frequency. As such, the traffic frequencies are isolated from the BCCH signal frequency, enabling new and novel interference reduction methods to be used amongst the traffic carriers.

For example, intelligent frequency hopping can be used, as the control channel cannot normally hop or it would be extremely difficult to make an initial synchronization to a signal that is transmitted at, for example, three different frequencies.

Further by example, intelligent power control can be used. In a synchronous network one can, for example, cause one base station to transmit with high power traffic channels at a certain timeslot, such as timeslot 1. In this case a neighbor base station would then assign the mobile station that was near to the base station to timeslot 1, since high interference from the first base station is to be expected.

Also by example, adaptive antenna solutions can be employed. That is, the BCCH signals must be transmitted over the entire cell area. However, traffic carriers could use beam forming to point the transmitted/received power to the correct mobile station position. When the BCCH signals are separated from traffic signals, in accordance with this invention, then the adaptive antenna solutions are more readily implemented.

It can thus be seen that the teachings of this invention provide for a separation of the high power synchronization, broadcast, common control signals from the traffic carriers. This, in turn, enables a variety of novel methods to be used to reduce or eliminate interference with the traffic carriers.

A novel multiplexed BCCH solution is thus provided by the teachings of this invention. More particularly, disclosed is a method for operating a wireless telecommunications system that includes steps of: (A) synchronously multiplexing a downlink communication frequency between transmissions of a plurality of base stations such that each base station transmits continuously for a plurality of consecutive time slot periods; and (B) receiving the transmission from at least one of the plurality of base stations with a mobile station, and transmitting an uplink transmission to one of the base stations from the mobile station during a time when the base station is not transmitting. The downlink transmissions from each of the plurality of base stations includes a Broadcast Control Channel (BCCH) signal. The method includes a further step of multiplexing random access uplink transmissions to the plurality of base stations so as to reduce latency. The step (A) of synchronously multiplexing preferably includes a step of inserting a guardtime period between transmissions of different ones of the plurality of base stations .

Further in accordance with a method for operating a wireless telecommunications system, this invention teaches performing steps of: (a) synchronously multiplexing a downlink control channel carrier (e.g., a 200 kHz bandwidth carrier) between X cell base stations such that each base station transmits continuously for a plurality of consecutive time slot periods; and (b) receiving the transmission from at least one of the X base stations with a mobile station, and transmitting an uplink transmission to one of the base stations from the mobile station during a time when the base station is not transmitting. The step of synchronously multiplexing includes a step of transmitting a frequency correction burst and a synchronization burst every N frames from M cells . In an exemplary embodiment N=26, M=4 and X=12. A frequency reuse plan is based on there being three traffic carriers and a single control channel carrier.

BRIEF DESCRIPTION OF THE DRAWINGS

The above set forth and other features of the invention are made more apparent in the ensuing Detailed Description of the Invention when read in conjunction with the attached Drawings, wherein:

Fig. 1 is a block diagram of an exemplary mobile station that is constructed and operated in accordance with this invention;

Fig. 2 is an elevational view of the mobile station shown in Fig. 1, and which further illustrates a wireless telecommunication system to which the mobile station is bidirectionally coupled through RF links;

Fig. 3 depicts a conventional GSM frame hierarchy;

Fig. 4 illustrates a multiplexed GSM BCCH transmission technique in accordance with this invention, wherein F = a frequency correction channel (FCCH) burst, S = a synchronization channel (SCH) burst, B = a broadcast control channel (BCCH) , C = a common control channel (CCCH) , R = a random access channel (RACH) , d = a stand alone dedicated control channel (SDCCH/X) signalling channel, where X indicates the subchannel number (one of four subchannels 0, 1, 2 and 3), and where s = a slow associated control channel (SACCH/X) signalling channel, where again X indicates the subchannel number (one of four subchannels 0, 1, 2 and 3);

Fig. 5 shows an example of how 12 cells can be multiplexed to a signal control carrier, where F = FCH = a Frequency Correction Burst, SCH = a synchronization burst, I = Idle = the guard time between cell changes, and B0-B11 = signalling blocks of the 52 -multiframe PBCCH+PCCCH;

Fig. 6 depicts a control channel and traffic channel reuse pattern with a 1/3 + 1 configuration; and Figs. 7A and 7B are graphs useful for contrasting signaling channel performance with 3/9 and 4/12 reuse (Fig. 7B is an enlarged portion of Fig. 7A) .

DETAILED DESCRIPTION OF THE INVENTION

Reference is first made to Figs. 1 and 2 for illustrating a wireless user terminal or mobile station 10, such as but not limited to a cellular radiotelephone or a personal communicator, that is suitable for practicing this invention. The mobile station 10 includes an antenna 12 for transmitting signals to and for receiving signals from a first base site or base station 30A (also referred to herein as a base transceiver station (BTS) ) , as well as a second and typically more base stations 30B. The base stations 30A and 30B can be a part of a cellular network comprising a Base Station/ Mobile Switching Center/ Interworking function (BMI) 32 that includes a mobile switching center (MSC) 34. The MSC 34 provides a connection to landline trunks when the mobile station 10 is involved in a call .

The mobile station 10 typically includes a modulator (MOD) 14A, a transmitter 14, a receiver 16, a demodulator (DEMOD) 16A, and a controller 18 that provides signals to and receives signals from the transmitter 14 and receiver 16, respectively. These signals include signalling information in accordance with the air interface standard of the applicable cellular system, and also user speech and/or user generated data. The air interface standard is assumed for this invention to be a TDMA type system of a type described in detail below, although the teaching of this invention is not intended to be limited only to this specific TDMA structure, or for use only with an IS-136 and/or GSM-type compatible mobile station. It is understood that the controller 18 also includes the circuitry required for implementing the audio and logic functions of the mobile station. By example, the controller 18 may be comprised of a digital signal processor device, a microprocessor device, and various analog to digital converters, digital to analog converters, and other support circuits . The control and signal processing functions of the mobile station are allocated between these devices according to their respective capabilities.

A user interface includes a conventional earphone or speaker 17, a conventional microphone 19, a display 20, and a user input device, typically a keypad 22, all of which are coupled to the controller 18. The keypad 22 includes the conventional numeric (0-9) and related keys (#,*) 22a, and other keys 22b used for operating the mobile station 10. These other keys 22b may include, by example, a SEND key, various menu scrolling and soft keys, and a PWR key. The mobile station 10 also includes a battery 26 for powering the various circuits that are required to operate the mobile station.

The mobile station 10 also includes various memories, shown collectively as the memory 24, wherein are stored a plurality of constants and variables that are used by the controller 18 during the operation of the mobile station. For example, the memory 24 stores the values of various cellular system parameters and the number assignment module (NAM) . An operating program for controlling the operation of controller 18 is also stored in the memory 24 (typically in a ROM device) . It should be understood that the mobile station 10 can be a vehicle mounted or a handheld device. It should further be appreciated that the mobile station 10 can be capable of operating with one or more air interface standards, modulation types, and access types. Having thus described one suitable but not limiting embodiment of a mobile station and radiotelephone system that can be used to practice the teachings of this invention, and referring now also to Fig. 4, the telecommunications network shown in Fig. 2 is assumed to be synchronous. That is, the various base stations 30 are enabled to transmit at specified times under the control of a master timing and synchronization source (TSS) or control means 33 (which could reside in the MSC 34 or anywhere within the BMI 32.)

In the example illustrated in Fig. 4 the control channel transmissions from two different base stations 30A and 30B are multiplexed to a single carrier frequency. BS 30A transmits during the first 6.5 TDMA frames and BS 30B transmits during the next 6.5 TDMA frames. There is a guardtime period (GP) of one timeslot duration between transitions from one base station transmission to the other. The use of the guardtime is preferred despite the use of the synchronous telecommunications network, as without the guardtime a mobile station 10 near BS 30B could receive the transmission from the more distant BS 30A because of signal delay. However, when each base station 30 is allowed to transmit more than just one burst (slot) in a transmit period, as in Fig. 4, then the required amount of guardtime between transmission periods is minimized.

As is illustrated in Fig. 4, the BS 30A transmits a normal GSM 51 multiframe BCCH data stream, whereas BS 30B transmits combined BCCH data. That is, Fig. 4 shows that both non-combined BCCH + CCCH and combined BCCH + CCCH + SDCCH/4 channel combinations can readily be used by the multiplexed BCCH teachings of this invention. A difference between the two channel combinations is that the non- combined BCCH channel combination cannot alone build a circuit-switched telephone call, as the SDCCH is needed at the beginning of a circuit switched call in order to setup initial dedicated signalling. The combined BCCH can be used in, by example, small cells where four simultaneous (4- SDCCH subchannels) call initializations are sufficient.

Uplink transmissions (mobile station to base station) are shifted so that the mobile station 10 is not required to transmit and receive simultaneously. The mobile station 10 responds with the BS 30A uplink only after the BS 30A downlink transmit period.

During the illustrated 13 TDMA frames the two base stations 30A and 30B are able to send and receive the same signalling data that they would handle using the normal GSM BCCH within 51 TDMA frames.

It should be noted that multiplexing eight cells (base stations) to one BCCH carrier frequency would require 52 TDMA frames (not the conventional 51 TDMA frames) , and that 52 TDMA frames is conveniently one half the measurement period in the conventional GSM system.

It should further be noted that the uplink RACH delay could possibly pose a problem with packet data. However, the uplink RACH burst allocation could be further multiplexed between the base stations, with the RACH bursts within an exemplary 6.5 TDMA frame uplink being allocated evenly between the two cells.

The teachings of this invention provide a number of advantages. For example, only one carrier is required to provide a significant level of effective frequency reuse. The actual number of cells transmitting at a single BCCH frequency can be made dynamic. That is, a dynamic assignment can be employed in the case where the system operator has a limited frequency spectrum, and where the operator may wish to set up, by example, 12-16 cells to each transmit their control channel at a single, common frequency. In general, the more cells that are multiplexed to one BCCH carrier frequency the smaller is the signalling capacity of each cell. However, if the operator can afford to use two frequencies for control channel signalling, then the average signalling speed is significantly increased over the one frequency case, while the frequency reuse factor would still be sufficient to assure the reliable operation of control channels.

In operation, the mobile station 10 receives the multiplexed BCCH carrier and synchronizes itself to the strongest transmit period. The mobile station 10 then decodes the BCCH block (composed of four bursts) to obtain information about the specific cell in which the mobile station 10 is about to camp. The BCCH block also contains information about another cell or cells which are multiplexed to the same BCCH carrier. This neighbor cell information could, for example, indicate that there are 12 cells multiplexed to this BCCH carrier frequency, and that the mobile station 10 should pay attention to cells 1, 5 and 8 for possible cell re-selection.

The teachings of this invention thus support neighboring cell receive level measurements also during circuit switched calls, since each involved base station 30A, 30B, etc. transmits more than one burst at a time.

Also, the mobile station synchronization and AGC problem mentioned above is avoided, as each base station transmits continuously for a certain period of time, enabling the mobile station more time to achieve synchronization and to adapt and settle its AGC circuitry. The teachings of this invention can be differentiated from other known types of proposed solutions due to a number of different factors, either taken alone or in combination. Several important distinctions are as follows.

First, the number of cells which are multiplexed to the single BCCH carrier can be dynamic, and there is no hard limit for the number of cells which can be multiplexed. The only limiting factor is the signaling channel delay, which increases when multiplexing more cells.

Second, the cells are multiplexed so that each cell transmits more than a single burst. This means that the mobile station 10 observes a continuous BCCH signal periodically from each cell over a number of consecutive time slots and TDMA frames. The guardtime between cell transitions is minimized by extending the cell transmitter active period (at the expense of increasing the signalling channel delay.)

Third, the uplink and downlink transmission for a particular cell also occur at different times, meaning the mobile station need not be a full duplex device.

The teachings of this invention can be further differentiated from other known types of proposed solutions by the fact that the uplink periods can be further multiplexed so that all the cells that are multiplexed to a particular carrier have a receive "slice" or period in each uplink period. In this way the random access delay is reduced as compared to a situation where only a single cell is receiving uplink data during an uplink period.

The foregoing teachings thus solve the above-described GSM BCCH problem, and further provide a technique to deploy 200 kHz GSM control carriers using a 1 MHz bandwidth, as opposed to the 2.5 MHz bandwidth currently specified for use in GSM systems .

In general, there are a number of considerations and functions that the control channel solution should satisfy. These include the following:

A first consideration is the data throughput on traffic channels, as the control channel should not disturb the data traffic. When the control channel is put on a traffic carrier the timeslot allocation for multislot terminals is difficult.

Another consideration is the adequacy of the signaling capacity. While there may be some comprises between 30 & 200 kHz reverse packet control channel signaling capacity, the forward packet control channel capacity is limiting in the case of an ETSI EDGE control channel. The 52 multiframe PBCCH+PCCCH has forward link signaling capacity of 12 blocks/ (52*0.004615) = 50 blocks/s, whereas the reverse PRACH capacity is 200 blocks/s. ETSI/EDGE control channel usage is different from 30 kHz PCCH usage. The ETSI/EDGE control channel is used only to give a channel assignment to a traffic channel, where further signaling is performed. This is opposite to 30 kHz control channel case, where the entire control signaling is done on the packet control channel .

Another consideration relates to providing reliable cell re-selection. As a general rule, the RX-level measurements from the control channel signal should not contain interference. However, when the RX-level is measured from a signal subject to very tight reuse (for example 1/3 reuse) the measurement results will always contain both signal and interference from neighbor signals. A further consideration relates to performing fast cell reselections (handovers) on the 200 kHz channel, as delay critical services (such as voice over IP solutions on the 200 kHz channel) require a fast cell reselection capability.

Another consideration is that the 200 kHz carrier should contain GSM multiframe synchronization information. Some prior proposals have suggested a PBCCH + PCCCH 52- multiframe control channel structure for the 200 kHz carrier. However, this channel combination does not contain multiframe synchronization information (SCH burst) . The situation is the same, as the coded super frame phase information would be absent from DCCH/PCCH downlink bursts.

Another consideration is that the mobile station 10 must be able to find the control channel without prior knowledge about the control channel frequency, such as when the mobile station is first powered on.

Other considerations include the ability to provide a hierarchical cell structure, and an ability to support ready expandability if more spectrum than 1MHz becomes available. Furthermore, a 200 kHz-only terminal should be able to roam on a 200 kHz 136HS control channel. If the 200 kHz control channel selection/re-selection requires a 30 kHz DCCH/PCCH, then 200 kHz-only terminals cannot camp on 136HS channels. Finally, the resulting solution should result in only minor changes to the ESI EDGE specifications .

The teachings of this invention beneficially provide a time multiplexed control channel solution for 136HS and other types of TDMA systems. The presently preferred time multiplexed control channel solution benefits a 200 kHz synchronized network. The basic idea is to multiplex control channels from multiple cells to a single frequency. Traffic channels may then be totally separated from the high power control channels, thereby providing more data throughput on 200 kHz traffic-only carriers. The single frequency, time multiplexed control carrier furthermore provides sufficient effective reuse for 200 kHz control channel operation.

This aspect of the invention us based on an ability to perform 200 kHz control channel cell selection/re- selection, thus also enabling 200 kHz-only terminals to camp on the 200 kHz carriers. Hierarchical 30 kHz and 200 kHz networks are also possible, since the 200 kHz carriers can survive without 30 kHz cell reselection.

A conventional ETSI/EDGE 52 -multiframe PBCCH+PCCCH structure can be modified to aid the initial synchronization and BSIC decoding, and the modifications involve just an addition of frequency correction and synchronization bursts. As a result, all of the higher level functionality of PBCCH+PCCCH logical channel is maintained unchanged.

This solution requires, in total, 600 MHz for 1/3 traffic channel reuse, and 200 MHz for the control channel.

As a further example of the instant teachings, reference is made to Fig. 5, where again the network is again assumed to be synchronous. In this example the control channel transmission from 12 different base stations (BTS) are multiplexed to single carrier, and each of the BTS transmit 6.25 TDMA periods at a time. There is one guard timeslot at the end of each BTS transmit period. The use of the guard time is preferred despite the use of the synchronous network, as without the guard time a mobile station 10 near to BTS2 could still receive transmissions from a distant BTS1 because of signal delay. However when each BTS is allowed to transmit more than one burst in a transmit period, then the required cumulative guard time between periods is reduced. The uplink and the downlink are further time multiplexed to reduce the mobile station 10 processing requirements, i.e., when BTS1 transmits, BTS2 receives, and vice versa.

In accordance with this aspect of these teachings a current ETSI/EDGE 52 -multiframe PBCCH+PCCCH structure is modified such that frequency correction bursts (FCH) are added at the beginning of each 6.25 TDMA transmit period. In addition, the PTCCH and one IDLE are removed. The PTCCH can be removed because the control carrier is used for control purposes only. The neighbor cell BSIC decoding is facilitated for the mobile station 10 also on the traffic channel when the synchronization bursts (SCH) occur every 26^th TDMA frame. Note that since every 26^th TDMA frame is used for transmitting the SCH bursts from four cells, the mobile station 10 is enabled to perform neighbor cell synchronization and BSIC decoding during traffic channel

IDLE TDMA frames that occur with the 26 TDMA frame period.

Fig. 6 depicts a control channel and traffic channel reuse pattern with the 1/3 + 1 configuration, wherein 12 cells are multiplexed to a single control channel frequency. There are three traffic carriers FI, F2 and F3 , and one control carrier F4. The control carrier is transmitted/received from each cell, but only at certain predetermined time periods. Fig. 6 illustrates how the mobile station 10 experiences the greatest power from the Tl transmit period on frequency F4. Interference from distant cells using the same time period is added to the same transmit period.

Based on these teachings, it can be appreciated that the above mentioned plurality of conditions are met and satisfied.

First, the data throughput is as high as it can be with 1/3 traffic channel reuse. All the timeslots can be allocated without restrictions as to traffic usage.

Second, the PBCCH+PCCCH control channel signaling capacity can be modified with parameters BS_PBCCH_BLKS, BS_PAG_BLKS_RES and BS_PRACH_BLKS . In the multiplexed control channel one can set the parameters so that all of the 12 blocks are reserved for signaling purposes. Then one many have the following signal rates :

with reuse 9 the downlink signaling capacity is 12 blocks/ (9*7*4.615ms) = 41.3 blocks/s (blocks per second),

with reuse 12 the downlink signaling capacity is 12 blocks/ (12*7*4.615ms) = 31.0 blocks/s, and

with reuse 15 the downlink signaling capacity is 12 blocks/ (15*7*4.615ms) = 24.8 blocks/s.

Furthermore, reliable cell reselections are made possible if, for example, 12 cells are multiplexed to a single frequency, as the mobile station 10 knows exactly the times when it can measure specific neighbors, and can also estimate the time difference between the serving cell and the neighbor cell from each neighbor measurement. The BSIC decoding can be done also during traffic time if the SCH burst can be received from the mobile station 10 monitoring window. This implies that a SCH burst should appear in all timeslots of a TDMA frame with a certain period.

Also, fast 200 kHz cell re-selections are made possible, as neighbor cell synchronization and BSIC decoding is supported also during traffic.

Furthermore, each of the multiplexed cell transmissions has both the FCH and SCH burst, enabling the mobile station 10 to synchronize to the 200 kHz carrier without 30 kHz carrier synchronization information. Since each base station 30 transmits for longer than one timeslot period, this facilitates the ability of the mobile station 10 to adjust its receiver gain to the correct level before actual synchronization and decoding of control channel data.

With regard to the initial synchronization problem mentioned above, the mobile station 10 must use more time to scan the frequency spectrum, as the mobile station 10 sees a periodically changing signal level from the multiplexed control carrier and can not rely on just simple received signal level measurement results. The initial control channel search is done only when mobile station 10 is switched on at a different network. This is because the mobile station 10 can store the last control channel frequency. The initial control channel search can be based on the highest received signal level measurement or on a frequency correction burst search. Specifying priority channel numbers to multiplexed control channels can accelerate both of those methods. For example, every fourth channel number can be a priority channel where the mobile station 10 could start the search. In the case of a dual mode mobile station 10 (e.g., 30 kHz and 200 kHz capable) the initial control channel search problem can be solved by reading pointers from 30 kHz DCCH to locate the 200 kHz control channel.

A hierarchical cell structure is made possible since cell re-selection does not rely on the 30 kHz signal.

Also, both the control channel reuse and traffic channel data capacity are readily expandable, as the control channels and the traffic channels are totally separated from one another.

In addition, 200 kHz-only terminals can roam both to 4/12 basic and 1+1/3 compact solution networks, as the 30 kHz carrier is not needed for synchronization or cell reselection .

Finally, the previously proposed single frequency, time multiplexed control channel requires larger changes to existing specifications (e.g., ETSI/EDGE) than the solutions presented herein. Furthermore, if the compatibility to the continuous BCCH is kept in mind, the teachings of this invention could be specified as a generic narrowband BCCH solution.

This invention thus provides a novel control channel solution for 200 kHz control channel based networks. The method uses optimally the synchronous network possibilities. The method enables a high data throughput as the control channel and traffic channels are separated. Furthermore, interference reduction methods such as frequency hopping, power control and adaptive antennas can be used on all eight traffic timeslots. Furthermore, all cell selection/reselection is based on the 200 kHz control channel, thereby enabling a 200 kHz-only mobile station 10 to roam. Hierarchical 30 and 200 kHz networks are also made possible. In addition, the time required to perform cell reselection is significantly reduced, thus enabling delay critical services on 200 kHz carriers to be realized. Also, the mobile station 10 complexity is reduced if fast mode changes are not required with 200 kHz cell reselection .

The graphs of Figs. 7A and 7B are useful for contrasting signaling channel performance with 3/9 and 4/12 reuse. These simulation results show the probability for a user to fall below a certain C/(I+N) signal. Only co-channel interference is taken into account. If one assumed, for example, a 10 dB C/(I+N) point from Fig. 7B (a zoomed version of Fig. 7A) it can be seen that with 3/9 reuse about 11% of all users in a cell have a C/(I+N) that is less than 10 dB . The same figure for 4/12 reuse gives 6%.

An exemplary ETSI/EDGE CSl coding scheme which is used with the PBCCH+PCCCH channel gives a 12.6% block error rate with a lOdB C/I signal (assuming no frequency hopping, and a typical urban 3 km/h channel model with 1900 MHz carrier frequency) . As a result, one can see that with a 3/9 reuse factor that about 11% of users will have unacceptable control channel performance.

The simulation assumptions reflected in Figs. 7A and 7B are as follows: (a) attenuation slope 3.76 (propagation formula is taken directly from UMTS 30.03) , (b) standard deviation of slow fading is 7 dB and the mean is 0 dB, (c) an antenna defined as in UMTS 30.03, (d) full loading, (e) noise -114 dBm, (f) TxP 10W (40 dBm) no power control, (g) site separation 6 km, diameter of a cell 4 km, and (h) a carrier frequency of 1900 MHz Although described in the context of preferred embodiments, it should be realized that a number of modifications to these teachings may occur to one skilled in the art.

For example, it should be noted that the 51-multiframe embodiment presented in Fig. 4 is but one possible embodiment of this invention. Actually, and in view of the fact that the novel multiplexed BCCH is not generally backwards compatible with existing GSM mobile stations, the multiframe structure could be totally redesigned. The example of Fig. 4 shows that both current GSM 51-multiframe BCCH + CCCH and BCCH + CCCH + SDCCH/4 channel combinations could be readily mapped, and there would thus be no need to change the upper layer software in the GSM- like network. One good starting point may be to take the current 52- multiframe PBCCH + PCCCH and add the FCH and SCH bursts to the IDLE positions. In addition, the control channel delay can be adjusted by changing the length of the transmit burst of each base station 30.

To summarize, it should be appreciated that the 51- multiframe embodiment of Fig. 4 is but one possible embodiment of the teachings of this invention and, in fact, represents one that would require a least amount of changes to the current GSM system. However, for optimum control channel performance the transmit period length and the actual contents of the transmit periods may be varied. As but one example, another embodiment of this invention could use a 52 -multiframe PBCCH + PCCCH with FCH and SCH added in the IDLE positions of PBCCH + PCCCH.

This invention thus provides a discontinuous transmission in a synchronous network, and the discontinuous control channel transmission/receptions are multiplexed to a single frequency. This leads to the following advantages.

First, the traffic channel and the control channel frequency planning can be performed separately (i.e., the control channel reuse plan can differ from the traffic channel reuse plan.

Second, since each cell is allowed to transmit more than a single burst period (when it is that cell's turn to transmit) the mobile station 10 can readily measure the control channel signal when operating on the traffic channels (i.e., the mobile station 10 sees a "continuous" signal periodically at the control frequency. Third, since the uplink and the downlink transmissions on the multiplexed control channel do not occur at the same time, the mobile station 10 is not required to be a full duplex device.

While the invention has been particularly shown and described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that changes in form and details may be made therein without departing from the scope and spirit of the invention.

Claims

CLAIMSWhat is claimed is:

1. A method for operating a wireless telecommunications system, comprising steps of:

synchronously multiplexing a downlink communication frequency between transmissions of a plurality of base stations such that each base station transmits continuously for a plurality of consecutive time slot periods; and

receiving the transmission from at least one of the plurality of base stations with a mobile station, and transmitting an uplink transmission to one of the base stations from the mobile station during a time when the base station is not transmitting.

2. A method as in claim 1, and further comprising a step of multiplexing random access uplink transmissions to the plurality of base stations so as to reduce latency.

3. A method as in claim 1, wherein the step of synchronously multiplexing comprises a step of inserting a guardtime period between transmissions of different ones of the plurality of base stations.

4. A method as in claim 1, wherein the step of synchronously multiplexing evenly divides A TDMA frames, each comprised of B slots, between the plurality of base stations .

5. A method as in claim 4, wherein A=13 and B=8.

6. A method as in claim 1, wherein the downlink transmission from each of the plurality of base stations includes a Broadcast Control Channel (BCCH) signal.

7. A method for operating a wireless telecommunications system, comprising steps of:

synchronously multiplexing a downlink channel between Broadcast Control Channel (BCCH) transmissions from a plurality of base stations such that each base station transmits continuously for at least one full TDMA frame; and

transmitting an uplink transmission to one of the base stations from a mobile station during a time when the base station is not transmitting.

8. A method as in claim 7, and further comprising a step of multiplexing random access uplink transmissions to the plurality of base stations so as to reduce latency.

9. A method as in claim 7, wherein the step of synchronously multiplexing comprises a step of inserting a guardtime period between transmissions of different ones of the plurality of base stations.

10. A method as in claim 7, wherein the step of synchronously multiplexing evenly divides 13 TDMA frames, each comprised of 8 slots, between the plurality of base stations .

11. A method for operating a wireless telecommunications system, comprising steps of:

synchronously multiplexing a downlink carrier frequency between synchronization/ broadcast/ common control channel transmissions from a plurality of base stations such that each base station transmits continuously for at least one full TDMA multiframe; and

receiving the downlink carrier frequency and decoding a transmission from a particular one of the base stations with a mobile station while camped within a cell of that base station, and also decoding a transmission from at least one other base station for cell re-selection purposes.

12. A method for operating a wireless telecommunications system, comprising steps of:

synchronously multiplexing a downlink control channel carrier between X number of cell base stations such that each base station transmits continuously for a plurality of consecutive time slot periods; and

receiving the transmission from at least one of the X base stations with a mobile station, and transmitting an uplink transmission to one of the X base stations from the mobile station during a time when the base station is not transmitting.

13. A method as in claim 12, wherein the step of synchronously multiplexing includes a step of transmitting a frequency correction burst and a synchronization burst every N frames from M cells.

14. A method as in claim 13, wherein N=26, and where

M=4

15. A method as in claim 12, wherein X=12.

16. A method as in claim 15, wherein a frequency reuse plan is based on there being three traffic carriers and a single control channel carrier.

17. A method as in claim 12, wherein a bandwidth of the control channel is about 200 kHz.

18. A synchronous wireless telecommunications system, comprising :

system control means for synchronously multiplexing a downlink control channel carrier between a X cell base stations such that each base station transmits continuously for a plurality of consecutive time slot periods ; and

a mobile station comprising a receiver for receiving the transmission from at least one of the X base stations, and further comprising a transmitter for transmitting an uplink transmission to one of the base stations during a time when the base station is not transmitting.

19. A system as in claim 18, wherein the downlink control channel carrier includes a frequency correction burst and a synchronization burst transmitted every N frames from M cells.

20. A system as in claim 19, wherein N=26, and where

M=4

21. A system as in claim 18, wherein X=12.

22. A system as in claim 18, wherein a frequency reuse plan is based on there being three traffic carriers and a single control channel carrier.

23. A system as in claim 18, wherein a bandwidth of the control channel is about 200 kHz.