Method, communication system and communication unit for synchronisation for multi-rate communication

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DESCRIPTION

Procedure, communication system and communication unit for synchronizing a communication with multiple rates

Field of the invention

The present invention relates to the field of digital communication systems and, specifically, to synchronization in digital communication systems such as wireless cellular communication systems. The invention finds particular application in modern digital wireless communication systems, such as Universal Mobile Communications Systems (UMTS).

Background of the invention

Synchronization is known to be an essential procedure in a modern digital communication system. It is the procedure used by a remote unit (often referred to as User Equipment, UE, in UMTS or User Facility Equipment, CPE) to identify valid transmissions from infrastructure equipment (often referred to as Node Bs in the UMTS) and align the remote frequency reference and timing by the utility with the infrastructure.

The UMTS Terrestrial Radio Access (UTRA) Time Division Duplexing (TDD) and Frequency Division Duplexing (FDD) modes both provide a synchronization channel (SCH) that is used by the UE to search for valid signals and carry out the synchronization procedure. The SCH transmission consists of a Primary Synchronization Code (PSC) and three Secondary Synchronization Codes (SSC), all with a length of 256 code segments. The PSC is common for all Node Bs, but the SSCs are specific to a Node B. The DSC and SSCs are transmitted simultaneously through a given Node B with a specific fixed time offset (tor / se) from the start of time slot 0. The time offset is included to prevent the possible capture effect that, otherwise, would occur as a consequence of the transmission by all Node Bs transmitting the common primary code at the same time .

The UE uses the PSC to search and identify the transmissions coming from Node B. The PSC is also used as a reference from which the UE is able to generate a correction that can be used to correct the frequency of the UE reference oscillator. The SSC is included to signal the additional information required by the UE in order to achieve the synchronization aligned in the total time and, likewise, to begin to demodulate the broadcasting of the system information on the Broadcast Channel (BCH) the which is transported by the Primary Common Control Physical Channel, P-CC-PH.

For code segment single rate systems in which the used code segment rate by the Node B and the UE is determined in advance by the system design, the synchronization procedure briefly outlined in the lines above is complete enough.

Document US 5950124 discloses the preamble of claim 1.

However, taking into consideration a network in which multiple code segment rates are supported, in an initial startup situation, the UE will not be aware of the code segment rate that may be available; therefore, the receiver in the UE is not able to select the correct code segment rate.

In some known systems, such as those using fixed line modems, the available bandwidth is negotiated in the initial data transfers between the sender and the receiver. This is done at a fixed transmission rate determined in advance, usually determined by design or by backward compatibility with design with early implementations.

Other possible designs could transmit the entire time slot in which the SCH bursts were transmitted at a lower code segment data rate (note that for a UMTS TDD system, the SCH is transmitted in each radio frame).

However, the known exposed scheme of the fixed initial rate negotiation and the other possible schemes have the disadvantage that they are inefficient.

Therefore, there is a need for a timing scheme for multi-rate communication in which the aforementioned drawback can be mitigated.

Declaration of the invention

According to a first aspect of the present invention, there is provided a method for synchronization in a multi-rate communication system, according to claim 1.

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According to a second aspect of the present invention there is provided a method for synchronization in a multi-rate communication system, according to claim 1.

According to a third aspect of the present invention there is provided a multi-rate communication system according to claim 13.

According to a fourth aspect of the present invention there is provided a communication unit, for use in a multi-rate communication system according to claim 20.

According to a fifth aspect of the present invention there is provided a communication unit, for use in a multi-rate communication system, according to claim 27.

Brief description of the drawings

A method, a communication unit, and a communication system for synchronizing a multi-rate communication incorporating the present invention will be described in the lines that follow, by way of example only, with reference to the accompanying drawings. , in which:

FIG. 1 shows a block diagram of a wireless communication system that can be adapted to support the various inventive concepts of a preferred embodiment of the present invention;

FIG. 2 shows a block diagram of a wireless communication unit that can be adapted to support the various inventive concepts of a preferred embodiment of the present invention;

FIG. F3 shows a schematic block diagram illustrating transmission and reception of SCH in a single code segment rate system embodying the invention;

FIG. 4 shows a schematic block diagram illustrating the transmission and reception of SCH in a code segment multiple rate system.

Description of the preferred embodiment

Referring now to FIG. 3, there is schematically shown a cellular-based wireless telephone communication system 100 with multiple code segment rates, in accordance with a preferred embodiment of the present invention. Preferably, the cellular based telephone communication system 100 is matched to, and contains, the network elements capable of operating over a UMTS air interface. In particular, the invention relates to the Third Generation Participation Project (3GPP) specification for a wideband code division multiple access (WCDMA) standard related to the UTRAN Radio Interface (described in the series of 25.xxx TS 3G specifications).

A plurality of subscriber terminals (or subscriber equipment (UE) in the UMTS nomenclature) 112, 114, 116 communicate via radio links 118, 119, 120 with a plurality of base transceiver stations, designated, in accordance with UMTS terminology as Node-Bs, 122, 124, 126, 128, 130, 132. The system comprises many other UEs and Node Bs, which for clarity are not shown.

The wireless communication system, sometimes referred to as the Network Operator's Network Domain, is connected to an external network 134, for example the Internet. The Network Operator's Network Domain includes:

(i) A core network, namely at least one Gateway GPRS Support Node (GGSN) 144 and / or at least one Serving GPRS Support Node (SGsN); and (ii) An access network, namely:

(ai) a GPRS (or UMTS) Radio Network Controller (RNC) 136 to 140; or (aii) a base site controller (BSC) in a GSM system and / or (bi) a GPRS (or UMTS) Node B 122 to 132; or (bii) a base transceiver station (BTS) in a GSM system.

The GGSN / SGSN 144 is responsible for interfacing the GPRS (or UMTS) with a Public Switching Data Network (PSDN) such as the Internet 134 or a General Telephone Communication network (PSTN) 134. An SGSN 144 it performs a routing and tunneling function for traffic within, say, a GPRS core network, while a GGSN 144 links to external packet networks, in this case, those that access the system's GPRS mode.

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Node Bs 122 to 132 are connected to external networks, by means of base station controllers, designated in UMTS terminology as Radio Network Controller (RNC) stations, which include RNCs 136 , 138, 140 and mobile switching centers (MSCs) such as MSC 142 (others for clarity not shown) and SGSN 144 (others for clarity not shown) .

Each Node B 122 to 132 contains one or more transceiver units and communicates with the rest of the cell-based system infrastructure via a lUB interface, as defined in the UMTS specification.

Each RNC 136-140 can control one or more Node Bs 122-132. Each MSC 142 provides a gateway to an external network 134. The Operations and Management Center (OMC) 146 is operatively connected to RNCs 136 through 140 and Node-B's 122 through 132 (shown only with respect to Node-B 126 for clarity). The OMC 146 administers and manages the sections of the cellular telephone communication system 100, as understood by those skilled in the art.

In the preferred embodiment of the invention, at least one UE 312 to 316 and at least one Node-B 322 to 332 is adapted to offer and provide the reception and processing of high speed signals with multiple transmission rates generated from according to the system discussed in detail below.

More specifically, in this embodiment, the exposed elements have been adapted to implement the present invention in both the reception and transmission modes of operation, in such a way that, in this embodiment, the invention can be applied both to transmissions is uplink as well as downlink.

It is also within the provisions of the invention that said adaptation of the physical level elements (air interface) can, as an alternative, be controlled, fully implemented or partially implemented by adapting any other appropriate part. of the communication system 100. For example equivalent parts in other types of systems may, in other circumstances, be adapted to provide some or all of the digital filtering implementation provided in the present embodiment.

Likewise, in the case of other network structures, the implementation of the processing operations can be carried out at any appropriate node, such as, for example, any other appropriate type of base station, base station controller, etc. .

Alternatively, the aforementioned digital filtering operations can be carried out by various components distributed at different locations or entities within any appropriate network or system.

Although the preferred embodiment of the invention is described with reference to a wireless communication system employing a UMTS air interface, it is within the scope of the invention that the inventive concepts described herein can be applied to any multi-bandwidth / multi-data rate communication system - fixed or wireless.

Referring now to FIG. 2, there is shown a block diagram of a communication unit 200, for example user equipment (UE) 112, adapted to support the concepts of the preferred embodiments of the present invention. However it is included in the provisions of the invention that a similar block diagram would apply to a Node B element, say Node B 122. Thus, in the description that follows, FIG. 2 it is described in such a way that it also encompasses an implementation of a Node B baseband processing circuit, in broad terms, as would be appreciated by the person skilled in the art.

The UE 112 contains an antenna 202 preferably coupled to a duplex filter or circulator or switch 204 that provides isolation between the receive and transmit chains within the UE 112.

The receiver chain includes receiver interface module scan circuitry 206 (efficiently providing reception, filtering, and baseband or intermediate frequency conversion). The interface module scan circuit 206 scans the signal transmissions from its associated Node B. The interface module scan circuit 206 is serially coupled to a signal processing function 208 (a processor, generally embodied in a DSP). The final receiver circuits are a baseband service circuit 209 operatively coupled to a display unit 210 if the communication unit is a subscriber unit.

Alternatively, if the communication unit is a Node B, the final receiving circuits are a baseband service circuit 209 operatively coupled to an interface port 210, in order to transmit the demodulated received signal to, say, a PC or an RNC.

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According to a preferred embodiment of the invention, the receiver chain, in particular the signal processing function 208 coupled to the baseband service scan circuit 209, has been adapted so that a receiving communication unit receives and process multiple high-speed signals of varying bandwidths.

A controller 214 is operatively coupled to the interface module scan circuit 206 so that the receiver can calculate the reception of the bit error transmission rate (BER) or the frame error transmission rate (FER) or similar link quality measurement data from information retrieved by means of a received signal strength indication (RSSI) function 212. The RSSI function 212 is operatively coupled to the interface module scan circuit 206.

A memory device 216 provided in the controller 214 stores a large array of UE-specific data, such as decoding / encoding functions, timing details, timing-related serving and neighboring cell information, channels, power control and the like, as well as link quality measurement information to enable an optimal communication link to be selected.

A timer 218 is operatively coupled to controller 214 to control the timing of operations, namely the transmission or reception of the time-dependent signals within the Ue 112.

In the context of the preferred embodiment of the present invention, the timer 218 is used to synchronize the timing of the receive communication unit 200 so that it is capable of switching between two or more filter configurations, as will be described. later, as well as to coordinate the appropriate signal clock input activation throughout the receiver.

For the sake of completeness, in general terms, the transmission chain of the communication unit (either a UE or a Node B) essentially includes an input device 220, coupled in series by means of the processor 208, a circuitry 222 transmitter / modulator and a power amplifier 224. Processor 208, transmitter / modulation circuitry 222, and power amplifier 224 are operatively responsive to controller 214, with an output from the power amplifier coupled to duplex filter or circulator 204, as is known. in technique.

The transmit chain signal processor function 208 may be implemented independently from the receiver chain processor. Alternatively, a single processor 208 may be used to implement processing of both the transmit and receive signals, as shown in FIG. 2.

Of course, it should be understood that the various components included within the communication unit 200 may be embodied in the form of discrete or integrated components, the final structure thus being a simply arbitrary selection.

In a more general sense, the digital filtering algorithms associated with the preferred embodiment of the present invention can be implemented in a respective communication unit in any appropriate way. For example, a new apparatus can be added to a conventional communication unit (e.g. UE 112 or Node B 122) or, alternatively, existing parts of a conventional communication unit can be adapted, e.g. by reprogramming one or more processors included within it. As such, the required adaptation can be implemented in the form of processor-implementable instructions stored in a storage medium on a data carrier, such as a floppy disk, a hard disk, a PROM, a RAM, or whatever. combination of these or other storage media.

The present invention, at least in a preferred form, implements a scheme in which the SCH channel at the UTRA air interface is transmitted at the lowest code segment rate supported by the system design. Note that only the SCH channel is always transmitted at the lowest code segment rate.

Since the SCH is transmitted at the lowest code segment rate, the receiving UE will default to the provision of the appropriate receiver bandwidth for this code segment rate. In this configuration, the UE It will be in a position to recover the SCH, regardless of the code segment rate used in the Node B transmission.

The data modulation on the secondary SCH defined by the UTRA standard does not use all the degrees of freedom available in the modulation scheme. Therefore, the mapping of the synchronization-specific data on the SSC can be expanded to make possible the additional signaling of the transmission of the rate of code segments of the Node B that must be added (see patent application GB n ° 0122109.2, filed on September 13, 2001 by the same applicant as the present application and entitled "ENCODER AND PROCEDURE FOR EFFICIENT CODING OF SYNCHRONIZATION CHANNEL IN TDD UTRA MODE" ["ENCODER AND METHOD FOR EFFICIENT SYNCHRONIZATION CHANNEL

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ENCODING IN UTRA TDD MODE ”], the contents of which are hereby incorporated herein by reference.

A simplified diagram of the single code segment rate implementation of an embodiment of the invention is shown in FIG. 3.

In this example, the SCH is treated identically to the rest of the data burst. That is, the SCH is processed by the same transmission and synchronization filters as the same channels used to transport the information that has the same code segment transmission rate.

In this way, as shown in FIG. 3A, in the transmission path of the transmission Node B a combiner 310 combines the information 320 from the SCH with the appropriate data burst structure 330. The resulting data burst containing the SCH information is filtered in digital low-pass transmit filter 340 (which may, for example, be of the "high-root cosine" type). The analog section 350 of the transmitter is set to the appropriate (narrower) bandwidth for the lowest code segment rate, and the data burst is sent to the antenna for transmission.

Correspondingly, as shown in FIG. 3B, in the receive path of the receiving UE, the analog section 360 of the receiver adjusts to the appropriate (narrower) bandwidth for the lowest code segment rate, and performs initial filtering of the data burst received at the antenna. The output of the analog section 360 is then filtered on the digital low pass receive filter 370 (which may, like the digital transmit filter 340, be of the "high root cosine" type). The output of the digital low-pass receive filter 370 is processed to retrieve the information from the SCH and (as will be discussed in greater detail later) to decode from it the information on the rate of the code segment. system (as represented in reference numeral 380). Since (in this single code segment rate assumption) the system code segment rate information does not indicate that the system code segment rate is different from the system code segment rate. code segments used for transmission of the SCH (that is, indicates that the single code segment rate is used), The digital filters of the receive path remain configured for the single lowest code segment transmission rate for the subsequent processing of the data burst (as indicated in reference numeral 390) and for the information of the transmission channel. transportation regarding SCH information.

Referring now also to FIG. 4, in the event that a different code segment rate is available for the physical channel that is used for transport data, it is necessary to provide different filters (or configure the filter (s) differently ) for the SCH channel and the physical channels used to transport the data. Said different filters, with the reconfiguration of the same filter (s), can be implemented as in GB patent application No. 018414.2, filed on July 30, 2001 by the same applicant as that of the present application and entitled "DIGITAL FILTER FOR THE COMMUNICATION OF MULTI-RATE COMMUNICATION" ["DIGITAL FILTER FOR MULTI-RATE COMMUNICATION"], the content of which is hereby incorporated herein by reference.

Suppose that the code segment rate in a multiple code segment rate system is given by:

fc = nfo; n =, ..., N where f_D is the base code segment data rate and N is the number of code segment rates available in the multiple code segment rate system. When a UE is initialized it knows a priori that the code segment rate being used for the SCH is fb, but it does not know the code segment rate of the system being used, fc. In the Node B transmitter it is necessary to pass the physical channel SCH through a filter (typically a digital filter) optimized for fb. The physical channels that support the data are filtered with a (digital) filter for the fc. In the analog section of the Node B transmitter, the filter bandwidth is always equal to fc.

In the reception section, the user equipment, the receiver bandwidth is adjusted to the fb in both the analog section and the digital sections. In this configuration, physical channels with the code segment rate fc may experience severe inter-symbol interference when fc ϊ fb. However, the physical channel of the SCH is received with minimal degradation. It is necessary to use a bandwidth of fb in the analog filter and in the digital filter in order to apply maximum attenuation to potentially high-power adjacent channel interferers.

With a UE in this configuration, it is possible to demodulate the SCH channel and decode the data carried by the SSC to determine the fc. When the initial synchronization has been achieved, the analog and digital filters are set to fc.

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FIG. 4 shows the receiver / transmitter implementation of the multi-code segment rate scheme.

In this way, as shown in FIG. 4A, in the transmission path of the transmission Node B a combiner 310 combines the SCH information 320 (filtered by a digital low pass filter 325 adjusted to the low data segment rate fb to ensure that the SCH information can be recovered at the receiver by filtering at the data segment rate) with the data burst structure 330 appreciated. The SCH information is encoded with the highest data segment transmission rate fc in the system, as discussed in detail in the aforementioned GB patent application No. 018414.2. The resulting data burst containing the SCH information is filtered in the digital low pass transmission filter 340 (now set for the high code segment rate fc). The analog section 350 of the transmitter is set to a bandwidth (wider than in the case of FIG. 3A) appropriate for the highest code segment rate. And the data burst is passed for transmission.

Correspondingly, in the receiving path of the receiving UE, in a first state, as shown in FIG. 4B, the receiver analog section 360 is set to the appropriate (narrower) bandwidth for the lowest rate of code segment transmission, and performs initial filtering of the received data burst at the antenna. The output of the analog section 360 is then filtered on the digital low-pass receive filter 370. The output of the digital low-pass filter 370 is processed to retrieve the sCh information and decode the system code segment rate information from it. It should be appreciated that the initial stage of receiving path processing is similar to that shown and described above in relation to the single code segment rate assumption shown in FIG. 3A. As will be discussed in greater detail later, at this stage (given that the indicated code segment transmission rate fc of the system is higher than the lowest code segment transmission rate fb used for the SCH ) data burst processing is disabled (as indicated in reference 395).

In this multiple code segment rate assumption, the system code segment rate information decoded from the SCH information indicates the highest code segment rate used for the system information. transport channel. Since this indicated systems code segment rate fc is higher than the low code segment rate fb used for SCH information, the information path is then configured in a second state, as shown in FIG. 4C, in which the analog section 360 and the digital low-pass receive filter 370 are set to appropriate bandwidths for the highest code segment rate fc.

In this second state, in the receiving path of the receiving UE, the analog section 360 of the receiver performs (now in the highest bandwidth appropriate for the highest transmission rate f_c code segment) filtering the signals received at the antenna. The output from the analog section 370 is then filtered (now at the highest bandwidth appropriate for the highest code segment rate fc) on the digital low-pass receive filter 370. The output of the digital low-pass receive filter 370 is then processed (i) to retrieve the data rate information (now enabled, as represented in reference numeral 390) and the transport channel information. at the highest transmission rate of code segments, and (ii) to process next (after filtering through a 385 digital low pass filter set to the low rate fb of code segments to ensure that the SCH information can be retrieved at the receiver by filtering at this rate code segment transmission) the SCH information (as represented in reference numeral 380).

It is to be understood that the method, communication unit and communication system for synchronizing a multi-rate communication described in the foregoing relationship provides improved efficiency in supporting multi-rate code segment support.