ier (SCID). Note that there are only three power- save modes in the legacy standard [1]. If an MS requests changes to the sleep pattern to one of the previous patterns using AAI_SLP-REQ including the associated SCID, the BS will respond with an AAI_SLP-RSP containing the same or a different SCID. There is only a single sleep cycle setting that is applied across all MS active connections. During the sleep window, the MS is unavailable to receive any DL data and MAC control signaling from the serving BS. For the duration of the listening window, the MS can receive DL data and MAC control signaling from the serving BS. The MS can also send data, if any uplink data is scheduled for transmission. The length of the listening window is measured in units of frames. After termination of a listening window, the MS may return to sleep for the remainder of the current sleep cycle. During the listening interval, if an MS does not have any downlink or uplink traffic in certain subframes (i.e., equal-sized fractions of radio frame), the MS can turn off its RF trans- mit/receive circuitry until the next active subframe(s) (as shown in Figure 6-20). These short-time sleep patterns are referred to as micro-sleep cycles and help the MS to further reduce power consumption. CHAPTER 6 The IEEE 802. 16m MAC CPS (Part I) Sleep Cycle Listening Window Sleep Window Radio Frame n Radio Frame n+1 Radio Frame n+2 Radio Frame n+3 Micro-sleep Periods FIGURE 6-20 Example of sleep cycles and micro-sleep patterns The serving BS may transmit the traffic indication message intended for one or multiple mobile stations during the listening window according to the Sleep Mode negotiation messages. It indicates whether there is traffic destined to one or multiple mobile stations. The traffic indication message is transmitted at a predefined location. On receiving a negative traffic indication in the traffic indication message, the MS can return to sleep for the remainder of the current sleep cycle. The duration of the listening window can be dynamically 