1. Field
The present invention relates generally to communications systems, and more specifically, to systems and techniques to optimize channel allocations in a communications systems.
2. Background
Modern communications systems are designed to allow multiple users to access a common communications medium. Numerous multiple-access techniques are known in the art, such as time division multiple-access (TDMA), frequency division multiple-access (FDMA), space division multiple-access, polarization division multiple-access, code division multiple-access (CDMA), and other similar multi-access techniques. The multiple-access concept is a channel allocation methodology which allows multiple user access to a common communications medium. The channel allocations can take on various forms depending on the specific multi-access technique. By way of example, in FDMA systems, the total frequency spectrum is divided into a number of smaller sub-bands and each user is given its own sub-band to access the communications medium. Alternatively, in TDMA systems, each user is given the entire frequency spectrum during periodically recurring time slots. In CDMA systems, each user is given the entire frequency spectrum for all of the time but distinguishes its transmission through the use of a unique code.
CDMA is a modulation and multiple access technique based on spread-spectrum communications. In a CDMA communications system, a large number of signals share the same frequency spectrum. This is achieved by transmitting each signal with a different code that modulates a carrier, and thereby, spreads the spectrum of the signal waveform. The transmitted signals are separated in the receiver by a correlator that uses a corresponding code to despread the desired signal's spectrum. The undesired signals, whose codes do not match, are not despread in bandwidth and contribute only to noise.
The use of CDMA techniques for multiple access communications generally provides increased user capacity over traditional TDMA and FDMA techniques. As a result, more users can access a network, or communicate with one another, through one or more base stations. In CDMA communications systems, the channel allocations are based on orthogonal sequences known as Walsh codes. Theoretically, maximum capacity of the CDMA communications system can be achieved when each available Walsh code is used to spread the traffic channels between multiple users. However, as a practical matter, numerous Walsh code channels may be required to support various control channels such as the pilot channel and other commonly used control channels. These control channels can generally be thought of as overhead which tends to consume bandwidth and decrease user capacity by reducing the number of Walsh channels available for traffic. With the tremendous increase in wireless applications over the past years, there is a need for a more efficient and robust data format which reduces overhead and increases throughput. This need is not limited to CDMA communications, but applies to various other communications systems.