Telecommunications – Carrier wave repeater or relay system – Portable or mobile repeater
Reexamination Certificate
2000-12-05
2004-08-31
Corsard, Nick (Department: 2684)
Telecommunications
Carrier wave repeater or relay system
Portable or mobile repeater
C455S013100, C455S502000
Reexamination Certificate
active
06785510
ABSTRACT:
BACKGROUND TO THE INVENTION
THIS invention relates to a method of routing transmissions within a multi-station network, typically between mobile stations in a cellular network utilising ad hoc or opportunistic message routing.
Such cellular systems consist of two primary families, namely Time Division Duplex (TDD) and Frequency Division Duplex (FDD) systems or hybrids of these two methods of duplexing. In the TDD system, base stations and mobiles achieve duplex or two-way communication through transmitting and receiving in sequential time slots, whereas in FDD duplexing is achieved by transmitting and receiving in different frequency bands.
In an ideal telecommunications system the minimum amount of transmit power would be used to cover a given path. In wireless telecommunications systems serving a large number of subscribers, an opportunistic method of transmission can be utilised, wherein information is relayed between a number of stations or nodes from an originating station to a destination station. An example of such a method is described in International patent application no. WO 96/19887 the contents of which are incorporated herein by reference.
In a system of the above kind, it has been shown that the most efficient method of communicating is to break a larger path down into a number of smaller hops, rather than to use a single relatively high powered hop. However, the efficient routing of data in such a system without incurring a large processing overhead is not trivial.
It is an object of the invention to address this issue.
SUMMARY OF THE INVENTION
According to the invention there is provided a method of relaying data between mobile stations in a cellular wireless communication system which comprises a plurality of mobile stations and a plurality of base stations, the method comprising the making of synchronisation transmissions from each base station within an area of coverage of the base stations, the synchronisation transmissions defining a broadcast control channel for the transmission of broadcast data from the base station to mobile stations within the area of coverage; receiving the synchronisation transmissions at mobile stations within the area of coverage and extracting data therefrom defining the broadcast control channel, and at least one calling channel on which mobile stations can transmit probe data to one another, the probe data being used by mobile stations to obtain connectivity information relating to the availability of other mobile stations.
The broadcast data transmitted from the base station to the mobile stations may contain information identifying the base station and information relating to available capacity at the base station.
The mobile stations may utilise the calling channel to broadcast probe signals to other mobile stations, the probe signals from each mobile station including information on the transmission power, local background noise level and path loss to other stations.
Preferably, mobile stations receiving probe signals from other mobile stations on the calling channel utilise the information therein to generate connectivity data relating to the other mobile stations.
The synchronisation transmissions preferably define at least one traffic channel usable by mobile stations to relay message data between themselves.
The synchronisation transmissions from the base stations are preferably made at relatively high power and a relatively low data rate, and message data transmitted between mobile stations on the traffic channel is transmitted at a relatively low power and a relatively high data rate.
In the method of the invention, high power, lower data rate transmissions are made by base stations which have wide area coverage and these transmissions are used for broadcasting synchronisation and other information directly to mobile stations within the cell (the area of coverage of the base station). The mobile stations operate at relatively low power and therefore need to relay message data from mobile station to mobile station to support high speed data services back to the base station from an originating mobile station within the cell. Relaying message data via mobile stations is also used to provide a high speed data service from the base station to a mobile station within the cell to effectively extend these services to the cell perimeter.
When mobile stations receive the synchronisation transmissions and broadcast data, they utilise this information to locate a specific time slot and frequency or “calling channel” (also referred to as a random access channel or ORACH) usable by mobile stations to interact with one another.
The mobile stations transmit so-called broadcast probe messages on the calling channel which contain several parameters, such as transmission power, local background noise level and path loss data. This information allows a mobile station receiving a broadcast probe message from a neighbouring mobile station to derive a local connectivity indicator for that neighbour. Each mobile station maintains a list of local connectivity indicators for each neighbouring station. This neighbour list is included in broadcast probe messages sent out by each mobile station, so that on receiving a broadcast probe message including a neighbour list, a mobile station can derive local connectivity information for other mobile stations up to two hops away.
Mobile stations also include gradient information in their probe messages. The gradient information represents the cumulative cost of transmitting data via a number of relay links to a particular destination station. A cost function is used to calculate the gradient for a particular destination. This function will depend on a number of parameters such as the cumulative power required to reach a designated destination station, resource utilisation on relay links, the number of relays required, etc. Each mobile station will update the gradient associated with a particular destination station every time it receives a probe message from a neighbour containing the destination station's identity data. As it is not practical for each mobile station to process and retain gradient information to every other mobile station, mobile stations use the synchronisation and broadcast transmissions from the base stations to identify which base station coverage area they are in, and develop gradients to those base stations. This significantly reduces the number of destinations that gradients are developed for, as normally a given mobile station will only be covered by one or a few base stations.
The synchronisation and broadcast information received from the base stations is used to define time slots and frequencies that can be used by mobile stations to transfer message data between themselves in relay mode. These time slots and frequencies are referred to as dedicated traffic channels (ODTCH).
The synchronisation of channels and resources is used by mobile stations according to the method of the invention to set up relay links to the base station more effectively.
DESCRIPTION OF AN EMBODIMENT
The method of the invention is primarily aimed at utilising so-called ODMA (opportunity division multiple access) techniques in a cellular wireless communication system in order to enhance the performance of such a system. The system is thus a hybrid between a conventional cellular system in which mobile stations communicate directly to a base station within a cell, and a full ODMA system in which there is not necessarily any base station and mobile stations communicate with each other by relaying messages amongst themselves.
The basic call process of the present invention can be summarised as follows:
If a mobile station MS
A
wishes to initiate a call to a base station:
1. The initiating mobile station MS
A
initially sends notification on the calling channel (ORACH) to its neighbors informing them to start developing gradients back to it. All stations in the area of coverage of the same base stations as MS
A
(established by monitoring the synchronization and broadcast transmissions from the bas
Corsard Nick
Ladas & Parry
Salbu Resarch & Development (Proprietary) Limited
Trinh Tan
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