| Method and apparatus for receiving site selection diversity transmit (ssdt) signal in a wideband code division multiple access (wcdma) system -> Monitor Keywords |
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Method and apparatus for receiving site selection diversity transmit (ssdt) signal in a wideband code division multiple access (wcdma) systemRelated Patent Categories: Telecommunications, Transmitter And Receiver At Separate Stations, Plural Transmitters Or Receivers (i.e., More Than Two Stations), Central Station (e.g., Master, Etc.), To Or From Mobile StationMethod and apparatus for receiving site selection diversity transmit (ssdt) signal in a wideband code division multiple access (wcdma) system description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070173272, Method and apparatus for receiving site selection diversity transmit (ssdt) signal in a wideband code division multiple access (wcdma) system. Brief Patent Description - Full Patent Description - Patent Application Claims
CLAIM OF PRIORITY FROM COPENDING PROVISIONAL PATENT APPLICATION [0001] This patent application claims priority under 35 U.S.C. .sctn.119(e) from Provisional Patent Application No. 60/468,471, filed May 6, 2003, the disclosure of which is incorporated by reference herein in its entirety. TECHNICAL FIELD [0002] This invention relates generally to cellular telephone systems, terminals and user equipment (UE) and, more specifically, relates to handover and soft handover techniques in a CDMA-based system. BACKGROUND [0003] There is currently specified a procedure known as SSDT (Site Selection Diversity Transmit power control) for use in a receiver of a WCDMA (Wideband Code Division Multiple Access) based system. The SSDT is a macro diversity method used in the soft handover mode, where the UE selects one of the cells from its active set of cells to be the primary cell. All other cells in the active set are then classified as being non-primary cells. The main objective is to transmit on the downlink (base station (BS) to UE) only from the primary cell, thus reducing the interference caused by multiple transmissions from other BSs in the soft handover mode. During conventional soft handover the UE can be simultaneously receiving transmissions from more than one BS. [0004] In order to select a primary cell, each cell is assigned a temporary identification (ID), and the UE periodically notifies connecting cells of the primary cell's ID. The non-primary cells selected by the UE switch off their transmission power. [0005] In the SSDT technique, as described above, the UE signals a desired Node B's Cell ID on the uplink using the DPCCH (Dedicated Physical Control Channel). In practical-deployment scenarios, however, there exists some non-zero probability for the occurrence of an error in the FBI (Feedback Information) bits that are used to transmit the Cell ID. Because of this non-zero error probability it can occur that the Node B signaled as the primary cell by the UE detects the code word erroneously, and thus does not assume the role of the primary cell for the signaling UE. In this a case the Node B does not transmit the downlink DPCH (Dedicated Physical Channel), as it interprets itself as being a secondary cell. As there is no downlink signalling to inform the UE as to which cell(s) have interpreted their role as being either the primary or the secondary cell, a UE functioning according to the current specification will attempt to receive the DPCH from the cell that the UE assumes to be the primary cell. However, a resulting attempt to decode non-existent bits (noise) on the downlink DPCH leads to an undesirable degradation in decoder performance. SUMMARY OF THE PREFERRED EMBODIMENTS [0006] The foregoing and other problems are overcome, and other advantages are realized, in accordance with the presently preferred embodiments of these teachings. [0007] Disclosed is a UE and a method to operate the UE in the Site Selection Diversity Transmit mode. The method includes detecting a case where no base station is transmitting to the UE; inserting predetermined values into a received signal; and decoding the predetermined values. The predetermined values preferably correspond to zero bits. [0008] In accordance with the method to operate the UE in the Site Selection Diversity Transmit mode the UE selects a primary cell and transmits an identification of the primary cell (Cell ID) using Feedback Information (FI) bits on a Dedicated Physical Control Channel (DPCCH). In response to detecting a case where the selected primary cell fails to transmit a downlink Dedicated Physical Channel (DPCH) to the UE, the UE inserts predetermined sample values into the output of a UE receiver prior to a UE channel decoder and decodes the predetermined sample values as zero bits so as to maintain proper channel decoder operation. BRIEF DESCRIPTION OF THE DRAWINGS [0009] The foregoing and other aspects of these teachings are made more evident in the following Detailed Description of the Preferred Embodiments, when read in conjunction with the attached Drawing Figures, wherein: [0010] FIG. 1 is a simplified block diagram an embodiment of a wireless communications system that includes a UE that is suitable for practicing this invention; [0011] FIG. 2 is a simplified block diagram of the receiver of the UE shown in FIG. 1; [0012] FIGS. 3A-3D are graphs that plot block error rate (BLER) versus E.sub.c/I.sub.or for various test cases; and [0013] FIG. 4 is a logic flow diagram that illustrates a method in accordance with this invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0014] By way of introduction, and referring to FIG. 1, there is shown as a simplified block diagram an embodiment of a wireless communications system 10 that is suitable for practicing this invention. The wireless communications system 10 includes at least one mobile station or UE 100. FIG. 1 also shows an exemplary network operator 20 having, for example, a node 30 for connecting to a telecommunications network, such as a Public Packet Data Network or PDN, at least one base station controller (BSC) 40 or equivalent apparatus, and a plurality of base transceiver stations (BTS) 50, also referred to as base stations (BSs), that transmit in a forward or downlink direction both physical and logical channels to the UE 100 in accordance with a predetermined air interface standard. A reverse or uplink communication path also exists from the UE 100 to the network operator, which conveys mobile originated access requests and traffic. A cell 3 is associated with each BTS 50, where one cell will at any given time be considered to be a serving cell, while an adjacent cell(s) will be considered to be a neighbor cell. In this invention the UE 100 will determine one of the cells 3A to be the primary cell, and the other cell(s) 3B to be non-primary cells, as was discussed above. [0015] The air interface standard can conform to any suitable standard or protocol, and may enable both voice and data traffic, such as data traffic enabling Internet 70 access and web page downloads. In the presently preferred embodiment of this invention the air interface standard is compatible with a WCDMA air interface standard, although this is not a limitation upon the practice of this invention. [0016] The UE 100 typically includes a control unit or control logic, such as a microcontrol unit (MCU) 120 having an output coupled to an input of a display 140 and an input coupled to an output of a keyboard or keypad 160. The UE 100 may be a handheld radiotelephone, such as a cellular telephone or a personal communicator. The UE 100 could also be contained within a card or module that is connected during use to another device. For example, the UE 10 could be contained within a PCMCIA or similar type of card or module that is installed during use within a portable data processor, such as a laptop or notebook computer, or even a computer that is wearable by the user. [0017] The MCU 120 is assumed to include or to be coupled to some type of a memory 130, including a non-volatile memory for storing an operating program and other information, as well as a volatile memory for temporarily storing required data, scratchpad memory, received packet data, packet data to be transmitted, and the like. At least some of this temporary data can be stored in a data buffer 130A. The operating program is assumed, for the purposes of this invention, to enable the MCU 120 to execute the software routines, layers and protocols required to implement the methods in accordance with this invention, as well as to provide a suitable user interface (UI), via display 140 and keypad 160, with a user. Although not shown, a microphone and speaker are typically provided for enabling the user to conduct voice calls in a conventional manner. [0018] The UE 100 also contains a wireless section that includes a digital signal processor (DSP) 180, or equivalent high speed processor or logic, as well as a wireless transceiver that includes a transmitter 200 and a receiver 220, both of which are coupled to an antenna 240 for communication with the network operator. At least one local oscillator, such as a frequency synthesizer (SYNTH) 260, is provided for tuning the transceiver. Data, such as digitized voice and packet data, is transmitted and received through the antenna 240. 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