In certain wireless communication systems, such as for example, cellular communication systems, network capacity and service coverage can be improved by using a plurality of smaller antennas at remote locations where a base station is not needed or desired. For example, such smaller antennas can be used in urban locations where Radio Frequency (RF) signals are degraded or blocked.
In this regard, a problem with cellular communications is that the radiated signals experience varying levels of degradation as they are transported over the radio air interface between a mobile station and a base station. Consequently, in order to extend service coverage and also compensate for such signal degradation, strategically-located wired or wireless signal repeaters are often used to receive, amplify and re-transmit the communication signals between the mobile stations and base station involved.
Unfortunately, a problem with the use of multiple antennas on the uplink (i.e., from the mobile station to the base station) is that each of the uplink antennas represents a noise source to the base station's receiver, and the overall noise floor is increased significantly as a result. The increased noise level interferes with the base station receiver's reception and detection of weaker signals from mobile stations that are located farther away. Consequently, service can become unavailable and communications can be blocked or dropped. More precisely, the uplink noise level is increased by 10*Log10 (N), where N represents the number of uplink antennas involved. Therefore, for example, if two uplink antennas are being used, the second antenna increases the uplink noise level by 10*Log10 (2) or approximately 3 dB.
Some approaches proposed for reducing the uplink noise floor recommend muting the uplink antenna paths during non-signal time periods when no traffic is being conveyed. However, a disadvantage of this approach is that muting an uplink antenna path increases the network's communication latency, by increasing the time it takes to restore the uplink connection and pass the signal from the mobile station to the base station (e.g., during a call initiation attempt). Consequently, the network's throughput and level of performance are reduced. Therefore, a pressing need exists for an approach that can be used to reduce the noise contribution of multiple uplink antennas in a wireless communication system, which also minimizes the effect on network throughput and level of performance for the system involved.