Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Reexamination Certificate
1998-09-10
2001-10-30
Vu, Huy D. (Department: 2663)
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
C455S446000
Reexamination Certificate
active
06310871
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to cellular communication systems and, more specifically, to a method for grouping and ungrouping sectors of a cell in a cellular communication system.
DESCRIPTION OF THE RELATED ART
In general, mobile communication systems such as Personal Communication Service (PCS) and Code Division Multiple Access (CDMA) communication systems include a plurality of Base Station Transceiver Subsystems (BTS) for serving mobile terminals, a plurality of Base Station Controllers (BSCs), a plurality of Base Station Manager Systems (BSMs) for managing and controlling the plurality of BSCs, a plurality of Mobile Switching Centers (MSCs), and a plurality of Home Location Registers (HLRs).
Cellular systems perform communications based on the cell unit. A cell is the geographic service area covered by a BTS. In general, a cell is classified as an omni-cell or a three sector cell. A mobile station communicates with a base station that supports the cell within which the mobile station is located. The communication is performed via forward and reverse communication channels. A forward communication channel is a channel that is formed from a base station to a mobile station, and includes a pilot channel, a synchronization channel, a paging channel, and a plurality of forward traffic channels. A reverse communication channel is a channel that is formed from a mobile station to a base station, and includes an access channel and a plurality of reverse traffic channels. The mobile and base stations exchange (transmit and receive) voice information and data through the traffic channels. The respective base stations are assigned frequencies according to system capacity, and utilize as many frequency channels as are assigned. The respective frequency channels are referred to as frequency assignments (FAs). A CDMA system includes several access channels by differing in the PN offset and the sequence per one frequency channel.
The systems under the mobile switching center with respect to hierarchy are conventionally referred to as base station subsystems (BSS). The base station subsystems include, in descending order, the BSM, the BSC, and the base stations. The main processors in the BSC and BTS are the call control processor (CCP) and the BTS control processor (BCP), respectively.
During operation, mobile stations should not suffer from communication failures when moving from region to region (i.e., cell to cell). Accordingly, when in an idle state, a mobile station should regularly re-register itself to the system according to various parameters. Further, in order to maintain sufficient efficiency with respect to the radio link when a call is in progress, the mobile station, base station and MSC manage the communication between the base station and the mobile station.
A CDMA communication system is capable of receiving mobile transmissions from two or more BTS at the same time. Additionally, a mobile station is capable of receiving signals transmitted from two or more BTSs at the same time. Due to these capabilities, handoffs can be conducted from one BTS to another BTS, or from one antenna region to another antenna region in a single BTS area. The term handoff refers to the processing procedure performed when a mobile station moves from one base station area to another base station area, or from one sector to another sector within a single base station area. During the handoff procedure, it is important that the call be maintained and also, that the quality of the voice information exchanged during the call not deteriorate. Accordingly, various types of handoffs are provided to ensure the continuity of a call in a CDMA cellular system and a PCS system. However, each type of handoff provides varying reliability with respect to maintaining the continuity of a call. Further, the load imposed on the CDMA and/or PCS system varies with each type of handoff.
The establishment and termination of a channel during a handoff procedure are referred to as an “add” and a “drop, respectively. In general, there are two types of handoffs, a soft handoff and a hard handoff. In a soft handoff procedure, which is also referred to as a make-before-break procedure, a new call is made before an existing call is broken (terminated). That is, a soft handoff is a procedure for setting up a communication path for a call wherein the mobile station communicates via two or more channels (to the serving cell and one or more target cells) to ensure the continuity of the call. In a hard handoff procedure, which is also referred to as a break-before-make procedure, an existing call is disconnected before a new call is made. In general, when a handoff is required because the mobile station is moving outside a cell boundary, a soft handoff is performed with respect to the call. However, in some unavoidable situations, a hard handoff is performed to ensure the continuity of the call. Nonetheless, because a CDMA system can concurrently establish multiple communication paths with different codes through identical frequency bands, soft handoffs are typically performed.
In a soft handoff procedure, when the signal strength of another communication path is greater than a threshold value, the mobile station concurrently communicates via the originally connected communication path and the new communication path. Then, the base station selects the best signal among the multiple signals of the multiple communication paths. When the signal strength of a particular communication path among the currently connected multiple communication paths becomes lower than a threshold value, the particular communication path is canceled.
Since a mobile station can concurrently establish two or more communication paths, the communication path having the best quality among the multiple communication paths is selected. As a result, the quality of the call is improved, and the continuity of the call is maintained. Additionally, by selecting the best communication path, the minimum necessary power is transmitted, thereby facilitating proper power control.
Upon receiving the appropriate communication signals, the receivers determine that transmission will begin soon, and set up a correct time reference for synchronization. At the time of synchronization, especially at the time when the system is initially synchronized, it is desirable to use signals which exhibit maximum autocorrelation functions at a 0 time shift and very small autocorrelation functions at all other time shifts.
For this purpose, it is possible to pre-store specific code words to the memory of the transmitter and the receiver. In addition, a binary shift register series generator, which is a relatively simple linear system, may be used to generate codes (i.e., binary sequences) which have sufficient autocorrelation characteristics. Shift registers are composed of serially connected binary memories. The binary values stored in the memories are transmitted to subsequent memories under the control of a clock pulse. Accordingly, the output of a three stage shift register is delayed by the time interval corresponding to three clock pulses. In any case, this shift register stores the most recent serial three bits among the input bit strings.
A binary shift register series generator has n stage shift registers, and an output which is fed back to the input of the generator and is connected to a logic combiner and several taps. A pseudo-random noise (PN) code generator, which is composed of n stage shift registers, can be employed to continuously generate n bit outputs of 2
n
−1 (the all zeros state is not included). The resulting bit sequence is referred to as a “PN sequence” because it appears to be random noise code except to those people who know the number of shift registers and taps employed. A PN sequence has very desirable autocorrelation properties since the maximum autocorrelation value of all the PN sequences is given at 0 shift and a reduced autocorrelation value is given at all other time shifts in one cycle. As a result, the power spectrum de
Boakye Alexander O.
Dilworth & Barrese LLP
Samsung Electronics Co,. Ltd.
Vu Huy D.
LandOfFree
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