Various types of wireless network are known that are able to communicate packet data. In CDMA technology, for example, such systems include EV-DO Rev. 0 and EV-DO Rev. 1. In general, reverse link access in CDMA systems is achieved by having users modulate their pilot and information signals on individually assigned spreading codes. Pilot and other control signals are code-multiplexed with data. In general, each user transmits a pilot signal in every timeslot.
In OFDMA technology, there are also wireless networks that can communicate packet data. Such networks include, for example, those that conform to the IEEE 802.16 standard. In general, OFDMA systems divide the total bandwidth available for reverse link transmission into narrow subcarriers. Groups of subcarriers collectively compose subchannels. In a given timeslot, each user may be allocated one or more subchannels which are orthogonal to each other and to subchannels allocated to other users. Subchannel allocations may change from one timeslot to the next. Each user transmits in bursts in those timeslots in which subchannels have been allocated to it. Certain subcarriers are allocated specifically for pilot signals. Each user transmits pilot signals in the pilot sub-carriers of the sub-channels assigned for data transmission.
Both the CDMA technology and the OFDMA technology suffer certain drawbacks. For example, interference between users tends to be relatively high in CDMA systems, and therefore might limit the total transmission rate on the reverse link. In OFDMA systems, on the other hand, a significant amount of signaling overhead is needed to support the assignment of subchannels. This limits the resources available for reverse link data transmission. In both technologies, users near the cell edge, which in general must transmit with relatively high power, tend to interfere with neighboring cells.
Thus, there remains a need for wireless systems, and in particular for wireless packet data systems, with still better reverse link performance.