In wireless communication systems, effort has been made to increase the use of spectrum to allow for a greater number of users of a given frequency band. One example of a technique to increase spectrum efficiency is a frequency division multiple access (FDMA) technique. In a conventional FDMA system, a given frequency band is divided into a number of channels, wherein each channel is occupied by one user. An FDMA system can also be a time division duplex (TDD) system wherein a given RF channel is used for transmitting frames in both the forward and reverse directions of communication which are separated in time.
Other techniques comprise digital multiple access communication systems. One such conventional digital multiple access technique for increasing efficient use of spectrum is a time division multiple access (TDMA) technique. In a TDMA system, each channel is divided into a plurality of slots for the transmission of signals. Each time slot may be allocated to a different call. A TDMA system can also employ TDD techniques. Accordingly, a number of calls can be simultaneously transmitted on a single channel or frequency.
Finally, increased spectrum efficiency can be achieved by spread spectrum techniques, in the form of either a slow frequency hopper system or a direct-sequence CDMA system. In a slow frequency hopper system, the carrier frequency of the signal is changed at a predetermined rate over a wide range of possible frequencies in a pseudo-random sequence known in advance by the receiver. Generally, spread spectrum techniques reduce the effects both intentional or unintentional interference. Direct sequence CDMA systems allow multiple users to share the same spectrum wherein each user is assigned a unique pseudonoise code sequence. The signal is spread by the wide bandwidth pseudo-noise sequence known in advance by the receiver.
In a conventional multiple access communication system, a base station periodically transmits a beacon or synchronization signal to maintain synchronization with an associated handset. For example, in a time division duplex multiple access system, a slot in a time frame must be occupied even if the base station is not in a call. Depending upon the communication system, available resources for providing communication between devices are used to maintain synchronization between devices which are not in communication. Accordingly, there is a need for a method and apparatus for increasing spectrum efficiency to allow a greater number of users to occupy a given frequency band.