Patent Application
20080153429
The present invention relates generally to compressed mode operation in a mobile communication system, and more particularly, to methods of controlling compressed mode operation by a plurality of mobile terminals.
A known problem with WCDMA phones is excessive power consumption that results in undesirable current drain and short battery life. When engaged in normal voice communications, a WCDMA phone transmits and receives continuously. This continuous operation is one of the primary reasons for the undesirable current drain in WCDMA phones. Another reason for current drain is the presence of a duplexer in the transmit path that increases path loss.
U.S. patent application Ser. No. 11/614,488 describes a method of reducing power consumption in a WCDMA phone by allowing the mobile terminals to switch to a compressed mode of operation. In the compressed mode, the mobile terminals transmit intermittently with a desired duty factor rather than continuously and increase their transmit power during the “on” periods to maintain the same data rate. Problems may arise with compressed mode operation if a significant number of users operate in a compressed mode at the same time. Because the mobile terminals normally increase their transmit power in compressed mode, they will interfere with other users if too many mobile terminals transmit at the same time in the compressed mode. Further, too many mobile terminals switching their transmitters on and off at the same time may result in undesirably large swings in the uplink load.
The present invention provides network-based methods to network manage compressed mode operation by a plurality of mobile terminals to distribute the uplink load resulting from compressed mode operation over time and to thereby reduce overall interference in the system resulting from compressed mode operation. Various methods are described with the same goal of avoiding synchronized transmissions of too many mobile terminals while in compressed mode. The base station or network monitors the uplink load and sends control signals to one or more mobile terminals to selectively enable and disable compressed mode operation. The base station can divide the mobile terminals into groups and can assign different compressed mode patterns to different groups of mobile terminals so that the transmissions from mobile terminals in different groups while in compressed mode are not synchronized. If load fluctuations occur, the network can reassign mobile terminals from one group to another to redistribute the load versus time.
The present invention provides a method of reducing power consumption in a radio communication system. The present invention is described herein in the context of a WCDMA radio communication system, though the techniques can be applied in other radio communication systems. Further, this application explains how the principles of the present invention can be applied to a voice channel in a WCDMA system. However, the principles described herein can be applied to other types of information, such as audio, video, and other data.
U.S. patent application Ser. No. 11/614,488 titled COMPRESSED MODE FOR REDUCING POWER CONSUMPTION filed Dec. 21, 2006 describes a method of reducing power consumption a WCDMA phone by allowing the mobile terminals 30 to switch to a compressed mode of operation. In the compressed mode, the mobile terminals 30 transmit intermittently with a desired duty factor rather than continuously, and increase their transmit power during the “on” periods to maintain the same data rate. This application is incorporated herein in its entirety by reference. To briefly summarize, the base station 10 continuously monitors the uplink load and sends control signals to one or more mobile terminals 30 to selectively enable and disable compressed mode operation depending on the uplink load. In general, compressed operation is enabled when the base station 10 has excess capacity on the uplink given the current loading conditions. If the uplink is heavily loaded, compressed mode is disabled. When the compressed mode is enabled, the mobile terminals 30 individually switch between the compressed mode (e.g. intermittent transmission) and normal mode (e.g., continuous transmission) on the uplink depending on the current transmit power level of the mobile terminal 30. When the current transmit power of the mobile terminal 30 is low and the mobile terminal 30 has sufficient power headroom, it uses compressed mode for uplink communications. Otherwise, the mobile terminal 30 transmits in normal mode on the uplink.
Problems may arise with compressed mode operation if a significant number of mobile terminals 30 operate in a compressed mode at the same time. Because the mobile terminals 30 normally increase their transmit power in compressed mode, they will interfere with other users if too many mobile terminals 30 transmit at the same time in the compressed mode. Moreover, if a large number of mobile terminals 30 switch their transmitters on and off at the same time, there will be pronounced swings in uplink load versus time.
The mobile terminals 30 may be allowed to randomly select slots in a defined transmission period to use for transmission in the compressed mode so that the transmissions from mobile terminals 30 operating in the compressed mode do not occur simultaneously. For example, each mobile terminal 30 may randomly select one or more compressed mode slots in the defined transmission period using the mobile terminal serial number as a seed to generate a random number. As used herein, the term compressed mode slot refers to slots in a defined transmission period when the mobile terminal 30 is transmitting. Other seed values could also be used as long as the seed value is not the same for a large number of mobile terminals 30. Random selection of compressed mode slots, however, is not the most effective method and may still result in undesirably high and uneven instantaneous loads.
According to the present invention, the base station 10 or other network node manages compressed mode operation by a plurality of mobile terminals 30 by assigning different compression patterns to different mobile terminals 30 or groups of mobile terminals 30. The compression pattern is an on/off pattern at the granularity of one slot that is used by the mobile terminals 30 while in compressed mode. The compression pattern may be designated by a sequence of binary values. For example, the pattern 1001 is a four slot pattern indicating that the mobile terminal 30 should transmit in slots 1 and 4 and turn off its transmitter in slots 2 and 3. The compression patterns may be designed such that the intermittent transmissions by the mobile terminals 30 are not all synchronized and are spread in time. Further, the compression patterns may be designed to avoid the simultaneous switching of transmitters on and off by too many mobile terminals 30, thereby avoiding large swings in uplink load versus time.
In some embodiments of the invention, compression patterns with different duty cycles may be assigned to different groups of mobile terminals 30. This approach is illustrated in
In one exemplary embodiment, the mobile terminals 30 are divided into groups and different sets of compression patterns are assigned to each group. Each group is assigned a set of compression patterns with different duty factors (e.g., 25%, 50%, 75%, etc.) that it may use for compressed mode operation. The compression patterns assigned to a particular group are not assigned to any other group. Thus, the compression patterns assigned to a particular group of mobile terminals 30 are unique to that group. As new mobile terminals establish calls, they are added to a group. When a mobile terminal 30 terminates a call, it is dropped from its group.
In compressed mode operation, the mobile terminals 30 select one of the compression patterns assigned to its group, depending on its power headroom. As new mobile terminals establish calls, they are added to a group. A mobile terminal 30 with limited power availability may select a compression pattern with a high duty factor (e.g., 80%), while another mobile terminal 30 with more power headroom may select a compression pattern with a small duty factor (e.g., 25%). The available duty factors and corresponding compression patterns can be predefined and stored in memory at the mobile terminal 30. When a mobile terminal 30 switches into a compressed mode, it selects a desired duty factor and a corresponding compression pattern from the available compression patterns.
There may be circumstances where usage patterns or other conditions outside the control of the base station 10 result in an undesirable variation in the uplink load. Variation in uplink load may be caused, for example, by variation in call duration for mobile terminals 30 in different groups and variation in the duty factors applied by mobile terminals 30 in different groups. Such variations may cause undesirably large fluctuations in uplink load. According to the present invention, the base station 10 may dynamically reassign mobile terminals 30 from one group to another to minimize fluctuations in uplink load versus time.
A further means to control the timing of uplink transmissions from the mobile terminals 30 can make use of all the previous methods, but instead of controlling the mobile terminal's uplink compressed mode pattern directly through a downlink control channel, may instead directly control the timing of the downlink compressed mode pattern. In this case, the mobile terminal 30 may select an uplink compressed mode timing with a fixed timing relationship to the downlink compressed mode timing. This method assumes that there is a downlink compressed mode being used along with an uplink compressed mode. Both uplink and downlink compressed modes do not have to have the same duty factor for this method of control to be effective. There only needs to be a known relationship between the timing of the uplink and downlink compressed modes in order for the base station 10 to be able to spread the uplink load versus time by means of controlling the downlink compressed mode timing to the plurality of mobile terminals 30.
The digital section 14 comprises baseband circuits 22 and a control circuit 24. The baseband circuits 22 and control circuit 24 may comprise one or more processors or processing circuits. The baseband circuit 22 processes signals transmitted and received by the base station 10. The baseband circuit 22 encode, modulate, and spread transmitted signals. On the receiver side, the baseband circuits 22 despread, demodulate, and decode received signals. The baseband circuit 122 also implements a vocoder (not shown) for encoding and decoding speech signals.
The control circuit 24 controls the overall operation of the base station 10. The control circuit 24 includes compression mode (CM) logic 26 for managing compressed mode operation as described herein. The CM mode control logic 26 selectively enables and disables compressed mode on the uplink and assigns mobile terminals 30 assigns mobile terminals 30 to groups.
The present invention provides a method and apparatus for substantially reducing power consumption in a WCDMA terminal. The present invention may be applied to either a mobile terminal or base station. When applied to a mobile terminal, the present invention results in longer battery life and talk times. The present invention is also beneficial in reducing overall interference in the network.
The present invention may, of course, be carried out in other specific ways than those herein set forth without departing from the scope and essential characteristics of the invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.
