Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1999-12-28
2003-11-11
Ho, Duc (Department: 2665)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S348000, C370S350000, C455S447000
Reexamination Certificate
active
06647000
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to cellular and wireless communication. More specifically, the invention relates to a system and method for introducing a communication system in a low frequency reuse pattern.
BACKGROUND OF THE INVENTION
Recently, there has been a trend in the telecommunication community to focus more and more on wireless packet data communication rather than circuit switched voice communication. With the tremendous increase of Internet users, it is believed that the packet switched communication will soon increase more and become larger than the circuit switched voice communication that today dominates, e.g., the cellular communication. Cellular communication system manufacturers and operators are therefore looking for solutions to integrate their circuit switched services with wireless packet switched services that can provide reliable and more spectrum efficient connections for packet switched users, e.g., Internet users. This trend has made different types of packet switched communication system evolutions flourish. One of the more well known packet switched cellular systems in the telecommunications community, is the extension of the present Global System for Mobile Communication (GSM), known as General Packet Radio Service (GPRS).
GPRS is a packet switched system that uses the same physical carrier structure as the present GSM cellular communication system and is designed to coexist and provide the same coverage as GSM. The GPRS radio interface is thus based on a TDMA (Time Division Multiple Access) structured system with 200 kHz carriers divided into eight timeslots with GMSK (Gaussian Minimum Shift Keying) modulation. The multiplexing is such that each timeslot can typically serve a number of users. One user can also be allocated more than one timeslot to increase its throughput of data over the air.
The GPRS specification includes a number of different coding schemes to be used dependent on the quality of the radio carrier. With GPRS, data rates well over 100 kbps will be possible.
There is also ongoing a development and standardization of a new air interface mode in GSM, which will affect both packet and circuit switched modes. This new air interface mode is called EDGE, Enhanced Data rates for Global Evolution. EDGE's main features are new modulation and coding schemes for both packet switched and circuit switched data communication. In addition to the Gaussian Minimum Shift Keying (GMSK) modulation, an 8 symbol Phase Shift Keying (8PSK) modulation is introduced. This modulation can provide users with higher bit rates than GMSK in good radio environments.
A new technique called link quality control is introduced with EDGE. Link quality control is a functionality that allows adaptation in terms of coding and modulation with respect to present signal quality. In poor radio conditions, a robust coding and GMSK modulation is selected whereas in good radio conditions, a less robust coding and 8PSK modulation is used. GPRS (and the extensions thereof) also provides a backward error correction functionality in that it can request retransmissions of erroneously received blocks. This mechanism is called ARQ (Automatic Repeat reQuest) and is well known in the art.
The packet data mode with EDGE modulation is called EGPRS (Enhanced GPRS) and the circuit switched data mode is called ECSD, Enhanced Circuit Switched Data. Bitrates over 384 kbps will be possible with EDGE.
Recent development for another TDMA based cellular system, the cellular communication system compliant to the ANSI/136 standard, below referred to as TDMA/136, has been focused on a packet data system to be integrated with the TDMA/136 circuit switched mode.
This packet data system will also be based on the new EDGE technology as defined for the GPRS extension. It will then allow TDMA/136 operators to provide bit rates up to 384 kbps on 200 kHz carriers with GMSK and 8PSK modulation as defined for EGPRS.
This integration of TDMA/136 and EDGE, does not, however, come without a cost. The TDMA/136 carriers have a bandwidth of only 30 kHz, to be compared with EDGE carriers of 200 kHz. This means that operators that want to introduce EDGE, have to allocate 200 kHz for each EDGE carrier or, to put it in another way, to free up spectrum for each EDGE carrier corresponding to 7 already existing 30 kHz carriers. Since operators already today are using these 30 kHz carriers for circuit switched communications, there is a large interest that the initial deployment for EDGE in TDMA/136 systems should be made on as small a spectrum as possible.
Reuse patterns are used in cellular systems, such that one can reuse the same frequencies in different cells. Systems are usually planned such that a number of cells share a number of available channels. For example, in a {fraction (4/12)} frequency reuse, there are {fraction (4/12)} different cells that share a set of frequencies. Within these 4/12 cells, no frequency is used in more than one cell simultaneously. (The number 4 in “{fraction (4/12)}” denotes the number of base station sites involved in the 12 reuse. The {fraction (4/12)} denotation thus indicates that a base station site serves 3 cells.) These 12 cells then form what is referred to as a cluster. Clusters are then repeated, to provide coverage in a certain area.
Similarly in a 1/3 reuse, there are 3 different cells that share a set of frequencies. Within these 3 cells, no frequency is used in more than one cell simultaneously. Thus, the higher the reuse, the better the carrier to interference ratio for an exemplary condition. For lower reuse patterns, the carrier to interference ratio is lower, since the distance between two base stations transmitting on the same frequency is shorter. An exemplary ⅓ reuse is illustrated in FIG.
1
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GPRS channels typically have different levels of robustness depending on the type of logical channel being transmitted. A logical channel is defined by its information content and is transmitted on one or several physical channels, defined by the physical channel structure, e.g., a timeslot on a certain frequency. In a packet data system, reliance on retransmission possibilities can allow a quite high error rate which means that the reuse for user data traffic channels can be kept quite low. For example, a data traffic channel can be deployed in a ⅓ reuse whereas common control channels and broadcast channels are not robust enough to be allocated in a ⅓ reuse, since the same retransmission possibilities are not used for these types of logical channels. At least a {fraction (3/9)} or even a 4/12 reuse is recommended for packet data common control and broadcast channels.
Note that a {fraction (3/9)} reuse entails that at least nine 200 kHz carriers are needed (i.e., TDMA operators must provide at least 1.8 MHz of spectrum for an initial deployment). This is considered quite substantial in a TDMA system with 30 kHz carriers.
This fact has driven the TDMA community to find other solutions for initial deployment of a packet data system based on EDGE and GPRS. U.S. Pat. No. 6,438,115 entitled, “High Speed Data Communication System and Method”, to Mazur et al., hereby incorporated by reference herein, teaches a method of combining TDMA/136 and the EGPRS mode of EDGE.
Briefly, the solution is to put requirements on the base station transmissions of the EDGE carriers. Base station transmissions of EDGE carriers should be time synchronised. It is then possible to allocate the control channels on different frequencies and different timeslots in different cells and thereby construct a higher reuse than what is possible by only considering frequencies. This solution is often referred to as EDGE Compact. In addition to the frequency reuse, a time reuse is introduced. For example, a certain base station transmits control signalling on a certain timeslot at a certain time and on a certain frequency, at which no other base station in the same control channel cluster (i.e., all cells where each physical channel carrying control signall
Lindheimer Christofer
Persson Bengt
Ho Duc
Telefonaktiebolaget LM Ericsson (publ)
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