Received communication signal processing methods and components for wireless communication equipment

This application is a continuation of U.S. patent application Ser. No. 10/794,126 filed Mar. 5, 2004, which claims the benefit of U.S. Provisional Patent Application No. 60/452,484, filed Mar. 5, 2003, U.S. Provisional Patent Application No. 60/452,342, filed Mar. 5, 2003 and U.S. Provisional Patent Application No. 60/452,343, filed Mar. 5, 2003 which are incorporated by reference as if fully set forth.

The present invention relates to methods and components for wireless communication equipment and, in particular, methods and components for facilitating initiation and maintenance of wireless communications.

Wireless telecommunication systems are well known in the art. In order to provide global connectivity for wireless systems, standards have been developed and are being implemented. One current standard in widespread use is known as Global System for Mobile Telecommunications (GSM). This is considered as a so-called Second Generation mobile radio system standard (2G) and was followed by its revision (2.5G). GPRS and EDGE are examples of 2.5G technologies that offer relatively high speed data service on top of (2G) GSM networks. Each one of these standards sought to improve upon the prior standard with additional features and enhancements. In January 1998, the European Telecommunications Standard Institute—Special Mobile Group (ETSI SMG) agreed on a radio access scheme for Third Generation Radio Systems called Universal Mobile Telecommunications Systems (UMTS). To further implement the UMTS standard, the Third Generation Partnership Project (3GPP) was formed in December 1998. 3GPP continues to work on a common third generational mobile radio standard.

A typical UMTS system architecture in accordance with current 3GPP specifications is depicted in FIG. 1. The UMTS network architecture includes a Core Network (CN) interconnected with a UMTS Terrestrial Radio Access Network (UTRAN) via an interface known as Iu which is defined in detail in the current publicly available 3GPP specification documents. The UTRAN is configured to provide wireless telecommunication services to users through wireless transmit receive units (WTRUs), known as User Equipments (UEs) in 3GPP, via a radio interface known as Uu. The UTRAN has one or more Radio Network Controllers (RNCs) and base stations, known as Node Bs in 3GPP, which collectively provide for the geographic coverage for wireless communications with UEs. One or more Node Bs are connected to each RNC via an interface known as Iub in 3GPP. The UTRAN may have several groups of Node Bs connected to different RNCs; two are shown in the example depicted in FIG. 1. Where more than one RNC is provided in a UTRAN, inter-RNC communication is performed via an Iur interface.

Communications external to the network components are performed by the Node Bs on a user level via the Uu interface and the CN on a network level via various CN connections to external systems.

In general, the primary function of base stations, such as Node Bs, is to provide a radio connection between the base stations\' network and the WTRUs. Typically a base station emits common channel signals allowing non-connected WTRUs to become synchronized with the base station\'s timing. In 3GPP, a Node B performs the physical radio connection with the UEs. The Node B receives signals over the Iub interface from the RNC that control the radio signals transmitted by the Node B over the Uu interface.

A CN is responsible for routing information to its correct destination. For example, the CN may route voice traffic from a UE that is received by the UMTS via one of the Node Bs to a public switched telephone network (PSTN) or packet data destined for the Internet. In 3GPP, the CN has six major components: 1) a serving General Packet Radio Service (GPRS) support node; 2) a gateway GPRS support node; 3) a border gateway; 4) a visitor location register; 5) a mobile services switching center; and 6) a gateway mobile services switching center. The serving GPRS support node provides access to packet switched domains, such as the Internet. The gateway GPRS support node is a gateway node for connections to other networks. All data traffic going to other operator\'s networks or the internet goes through the gateway GPRS support node. The border gateway acts as a firewall to prevent attacks by intruders outside the network on subscribers within the network realm. The visitor location register is a current serving networks ‘copy’ of subscriber data needed to provide services. This information initially comes from a database which administers mobile subscribers. The mobile services switching center is in charge of ‘circuit switched’ connections from UMTS terminals to the network. The gateway mobile services switching center implements routing functions required based on current location of subscribers. The gateway mobile services also receives and administers connection requests from subscribers from external networks.

The RNCs generally control internal functions of the UTRAN. The RNCs also provides intermediary services for communications having a local component via a Uu interface connection with a Node B and an external service component via a connection between the CN and an external system, for example overseas calls made from a cell phone in a domestic UMTS.

Typically a RNC oversees multiple base stations, manages radio resources within the geographic area of wireless radio service coverage serviced by the Node Bs and controls the physical radio resources for the Uu interface. In 3GPP, the Iu interface of an RNC provides two connections to the CN: one to a packet switched domain and the other to a circuit switched domain. Other important functions of the RNCs include confidentiality and integrity protection. Background specification data for such systems are publicly available and continue to be developed.

In general, commercial wireless systems utilize a well defined system time frame format for the transmission of wireless communication signals. In communication systems such as Third Generation Partnership Project (3GPP) Time Division Duplex (TDD) and Frequency Division Duplex (FDD) systems, multiple shared and dedicated channels of variable rate data are combined for transmission. However, irrespective of whether a system is based on TDD or FDD, received wireless signals must be decoded in accordance with the timeframe structure with which they are transmitted.

One of the first tasks to be performed in the initiation of a wireless communication is to determine the relative timing of a received signal for synchronization. In modern systems, there are various levels of synchronization, such as, carrier, frequency, code, symbol, frame and network synchronization. At each level, synchronization can be divided into two phases: acquisition (initial synchronization) and tracking (fine synchronization).

A typical wireless communication system, such as specified in the 3rd Generation Partnership Project (3GPP), sends downlink communications from a base station to one or a plurality of User Equipments (UEs) and uplink communications from UEs to the base station. A receiver within each UE operates by correlating, or despreading, a received downlink signal with a known code sequence. The code sequence is synchronized to the received sequence in order to get the maximal output from the correlator.

A receiver may receive time offset copies of a transmitted communication signal known as multi-path. In multi-path fading channels, the signal energy is dispersed over a certain amount of time due to distinct echo paths and scattering. To improve performance, the receiver can estimate the channel by combining the multi-path copies of the signal. If the receiver has information about the channel profile, one way of gathering signal energy is then to assign several correlator branches to different echo paths and combine their outputs constructively. This is conventionally done using a structure known as a RAKE receiver.

Conventionally, a RAKE receiver has several “fingers”, one for each echo path. In each finger, a path delay with respect to some reference delay, such as the direct or the earliest received path, must be estimated and tracked throughout the transmission. The estimation of the paths initial position in time may be obtained by using a multi-path search algorithm. The multi-path search algorithm does an extensive search through correlators to locate paths with a desired chip accuracy. RAKE receivers are able to exploit multi-path propagation to benefit from path diversity of transmitted signal. Using more than one path, or ray, increases the signal power available to the receiver. Additionally, it provides protection against fading since several paths are unlikely to be subject to a deep fade simultaneously. With suitable combining, this can improve the received signal-to-noise ratio, reduce fading and ease power control problems.

During reception, it is not always possible to separate the received energy into components attributable to distinct multipath components. This may happen, for example, if the relative delays of the various arriving paths are very small compared to the duration of a chip. Such situations often arise in indoor and urban communication channels. The problem is often referred to as the “Fat Finger Effect.” Accordingly, RAKE receivers have been developed that are capable of identifying the Fat fingers, such as the RAKE receiver disclosed in U.S. patent application. Ser. No. 10/304,894, RECEIVER FOR WIRELESS TELECOMMUNICATION STATIONS AND METHOD published as Publication No. US-2003-0157892-A1 on Aug. 21, 2003 and owned by the assignee of the present invention. FIG. 2 is an illustration of the processing of a received wireless communication signal with a preferred RAKE receiver that includes Fat finger allocation.

As illustrated in FIG. 2, the received wireless communication system is subject to an initial cell search preprocessing before RAKE finger allocation. The initial preprocessing identifies reception of a specific signal sequence such as a pilot sequence or, for example, a preamble sequence of a Random Access Channel (RACH). Various methods of searching for and identifying known transmitted signal sequences are know in the art. For example, such methods and apparatus are disclosed in U.S. patent application Ser. No. 10/322,184, APPARATUS AND METHOD OF SEARCHING FOR KNOWN SEQUENCES published as Publication No. US-2003-0161416 on Aug. 28, 2003 and owned by the assignee of the present invention.

There are several purposes why a sequence of symbols known to the receiver might be sent out from a transmitter, for example, channel estimation with respect to timing delay, amplitude and phase such as in a path search; signaling for (slotted) ALOHA multiple access collision detection and access granting such as with RACH preamble detection; and signaling of timing relations and even code group allocations, such as in a cell search.

In cases where lower level signaling is involved, there are usually several different known sequences that possibly can be sent out, and the signaling value is dependent on which one is found. Therefore, the search has to be performed over all available possible, or relevant, sequences.