It is known in wireless communications systems to provide various channels for communications between a base station (BS) and remote stations any one of which may be mobile and accordingly is referred to as a mobile station (MS). Such channels include, for example, both dedicated and shared traffic channels and control channels, for either or both of a forward link from a BS to an MS and a reverse link from an MS to a BS.
In known wireless systems an MS can have individually assigned to it, at call set-up or subsequently, forward and/or reverse dedicated channels for packet data communications, as well as dedicated traffic and dedicated control channels. In order to save battery power, it is known to provide a control hold mode for an active user for which a data buffer has been empty for a period of time. In the control hold mode, the high data rate supplemental channel is released and the forward and reverse dedicated control channels communicate only the pilot and power control signals (i.e. data acknowledgements are not sent) at either a full rate (the time slot rate) or a reduced rate.
In more recently proposed wireless systems there are shared traffic channels, shared control channels, and common power control channels; these known systems do not provide a control hold mode.
In these more recent systems, for example high rate packet data communications are provided on a high rate forward channel, referred to as the forward packet data channel or F-PDCH, which is shared by time division multiplexing among multiple active users and which may for example have a constant RF power. For example, with time slots of 1.25 ms, such a high rate channel may be allocated to different users (MSs) in different time slots. Each such MS is assigned a MAC (medium access control, OSI Layer 2) identifier (MAC_ID) which is transmitted in corresponding time slots on a shared control channel, referred to as a forward packet data control channel or F-PDCCH, to identify the MS for which the data on the F-PDCH is intended. A forward link scheduler provides rate control by scheduling packet data to the user who has the most favourable forward link channel condition.
In a full-queue situation in which network-side data buffers for all active users are always occupied, such an arrangement can provide significant multi-user diversity gain. However, in a more realistic non-full-queue situation in which active users' buffers are not always occupied by data, the multi-user diversity gain decreases significantly because an active user's buffer may be empty although the user has the most favourable channel condition.
In response to a user requesting a packet data communications session, the system transitions the user to an active state through dedicated or shared resource assignments. The system resources involved include a sub-channel of a forward link common power control channel or F-CPCCH, which the MS of an active user detects for the purpose of closed-loop reverse link power control, the F-PDCCH and F-PDCH referred to above, and reverse link dedicated channels R-PICH, R-CQICH, and R-ACKCH for control signalling required for supporting the forward link high rate data transmissions. When a user is in the active state, the MS sends a pilot on the reverse pilot channel R-PICH and feedback information including a channel condition (C/I or carrier-to-interference ratio report) indicating the quality of the forward link on the reverse channel quality indication channel R-CQICH, and an ACK/NAK (acknowledgement or negative acknowledgement) indication for an ARQ (automatic retransmission) function on the reverse acknowledgement channel R-ACKCH. This reverse link information is updated in each timeslot, i.e. at a rate of 800 Hz for a time slot duration of 1.25 ms. The sub-channel of the F-CPCCH is also detected at this time slot rate of for example 800 Hz.
Although it is conceivable to increase the number of active users thereby to increase the multi-user diversity gain in non-full-queue situations, the number of active users that can be supported is restricted by these limited system resources for overhead information for active users.
It is desirable to facilitate an increase in the number of active users without increasing the associated system resources for overhead information required for supporting active users.