With the increasing demand for wireless services, contention for limited radio spectrum is becoming an important issue. In particular, it is anticipated that there will be an increasing demand for data services. An example of the larger bandwidth needed for data is the UMTS radio system UTRAN (a trade name for CDMA air interface standards aimed at 3G (third generation) requirements) having a channel Bandwidth=5 MHz while other current and future systems such as IS-95 or 1XRTT (channel Bandwidth=1.25 MHz) have been optimized for voice services. Because of expanding needs for both voice and data services, there has been some interest in developing an RF receiver than can handle signals having different air interfaces and different RF channel bandwidths.
It is well known that it is difficult to mix voice and data services and provide a common radio system or modem that handles both. Ideally, a system should be able to provide both voice and data services efficiently and simultaneously. In conventional systems, the performance of one is often optimized at the expense of the other because the voice service generally requires a circuit mode of operation while the data service requires a packet mode of operation.
One current solution is to provide both voice and data using the same modem. This is often done at the expense of system capacity and performance. These systems use two different radio systems with one optimized for voice, occupying a particular section of the frequency spectrum, and the other optimized for data, occupying another (generally adjacent) part of the spectrum. This solution has certain difficulties including that 1) a large amount of spectrum is required and 2) it is necessary to switch between voice and data services. Further, the switching can be slow because of the need for hard hand over, that is, during hand over, the RF front end is required to switch frequency, causing some delay.
These current solutions do not offer simultaneous use of voice and data services and thus may result in wasted spectrum if the mix of voice and data traffic changes (e.g. when there is only data traffic, the voice spectrum is not used).
Further, when planning the design of new radio systems it is also important to consider the transition between a previous generation and newer systems and services. As traffic from users shifts from voice to data, for example, system operators may wish to use their radio spectrum to provide a different combination of services. In this case, it would be advantageous for the channels for these services to overlap as the cost of new spectrum and equipment may be expensive. The development of a suitable radio system that allows two or more radio systems to share overlapping spectrum and that adapts to changes in the traffic (i.e. from voice to data) is thus an important element in the development of future generation radio systems.