1. Field
The present invention pertains generally to communications, and more specifically to a novel and improved method and apparatus for hashing over multiple frequency bands in a communication system.
2. Background
Communication systems and wireless systems in particular, are designed with the objective of efficient allocation of resources among a variety of users. Wireless system designers in particular aim to provide sufficient resources to satisfy the communication needs of its subscribers while minimizing costs. Efficient use of resources requires prompt assignment of mobile stations to specific frequencies.
In a wireless communication system employing a Code Division-Multiple Access (CDMA) scheme or Wideband Code Division Multiple Access (WCDMA) each of the subscriber units is assigned code channels at designated time intervals on a time multiplexed basis. A central communication node, such as a Base Station (BS) or Node B, implements the unique carrier frequency or channel code associated with the subscriber to enable exclusive communication with the subscriber. Time Division Multiple Access (TDMA) schemes may also be implemented in landline systems using physical contact relay switching or packet switching. A CDMA system may be designed to support one or more standards such as: (1) the “TIA/EIA/IS-95-B Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System” referred to herein as the IS-95 standard; (2) the standard offered by a consortium named “3rd Generation Partnership Project” referred to herein as 3GPP; and embodied in a set of documents including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214, 3G TS 25.302, referred to herein as the W-CDMA standard; (3) the standard offered by a consortium named “3rd Generation Partnership Project 2” referred to herein as 3GPP2, and TR-45.5 referred to herein as the cdma2000 standard, formerly called IS-2000 MC, or (4) some other wireless standard.
CDMA2000 is an improvement on TIA/EIA-95. It provides a significant improvement in voice capacity and extended data capability and is backward compatible with TIA/EIA-95 mobiles. When a mobile station moves between base stations in a CDMA2000 system the mobiles must register and be assigned a frequency for communication. The frequency assignment occurs during a registration process. Registration includes a hashing process to assign a frequency to the mobile station. The mobile must re-register when changing between base stations, with each change forcing a new hash to a new frequency, and in many cases a new frequency band. Hashing is triggered for any change in the frequency distribution or frequency weights. Frequency distribution and weighting is an important consideration for balancing system loading and ensuring efficient system operation. The mobile station also updates the system overhead information each time a hash is performed. This can result in additional and excessive frequency changes, as every frequency change results in system acquisition and reading system overhead information. Unfortunately, while re-acquiring the system pages messages directed to the mobile station may be missed.
Accordingly, there is a need for a method and apparatus for hashing mobiles over multiple bands while avoiding unnecessary frequency changes.