This invention relates to wireless communications systems and, more particularly, to wireless communications between mobile units and base stations.
The basic mechanism in wireless communication systems for a base station and one or more mobile units to communicate is to exchange messages by utilizing a so-called segment. One such wireless system is the Orthogonal Frequency Division Multiplex (OFDM) system. A segment, as shown in FIG. 1, is a combination of a time slot index and a waveform index. A time slot is a basic time unit having a unique time slot index associated with it. During any particular time slot interval there could be several waveforms that are transmitted and received that may or may not be orthogonal. Each waveform has a unique waveform index. Messages of particular interest in wireless communication systems are mobile unit requests on an uplink.
Typically, the same uplink resource is shared by more than one mobile unit to convey access requests to a base station. As shown in FIGS. 2A and 2B, different mobile units may be assigned segments that have the same time slot index, and either the same waveform index or different waveform indices, but the waveforms are not orthogonal. In FIG. 2A one mobile unit, for example #1, is transmitting a request while Ar another mobile unit, for example #2, is not. Consequently, there is no collision between the request from mobile unit #1 with a request from mobile unit #2. However, since requests from the individual mobile units may arrive at a base station randomly, there is a distinct possibility of a collision between requests from mobile unit #1 and mobile unit #2, as shown in FIG. 2B. Consequently, both requests must be re-transmitted resulting in undesirable delay.
Moreover, because there is no power control of the mobile unit during the access request process and because the nature of the request transmissions is random and bursty, the uplink request process is very slow and its reliability is less than desirable.
Problems and limitations of prior mobile unit and base station access request transmissions are addressed by assigning each mobile unit a unique dedicated uplink resource. Specifically, each mobile unit is assigned segments with distinct time slot indices and/or waveform indices, where waveforms with distinct indices are orthogonal.
A base station can identify the mobile that has made an access request from the dedicated uplink resource. Therefore, no mobile identification number is needed in the uplink request message. Then, the base station can transmit a request response message on a shared downlink resource that may include the identification number of the requesting mobile unit to acknowledge reception of the request.
The mobile unit may transmit on a shared uplink resource an acknowledgment of reception of the downlink request response message.