The F-QPCH is a new physical channel used in IS-2000 to improve the efficiency of sending page messages. The IS-95 F-PCH, while effective, does have some drawbacks:
• In the nonslotted mode the mobile has to monitor continuously the entire pag-
ing channel slot, which in IS-95 lasts 80 ms. As a result, the mobile expends a lot of battery power to perform this continuous monitoring.
• In the slotted mode the mobile monitors only those time slots that are assigned
to it. While this does save some battery power, it is still inefficient. From the base station’s perspective, it is inefficient because when the base station has a
20-ms frame (9.6 Kbps) 5-ms frame (9.6 Kbps) 172 information bits 24 information bits 8 encoder tail bits 12 CRC bits 8 encoder tail bits 16 CRC bits
mobile-specific page to send, it cannot immediately send it. The base station has to wait for the correct slot to come along to send the page. As a result, the mobile often does not receive its designated pages immediately. From the mobile’s perspective, while the mobile saves some battery power by only monitoring its assigned slot, the assigned slot still lasts 80 ms. At the begin- ning of its assigned slot, the mobile still has to wake up to monitor the entire 80-ms slot, and most of the time there is no page directed at the mobile.
In IS-2000, the F-QPCH is added to alleviate the drawbacks cited above. If there is a page directed to a mobile, the base station first uses the F-QPCH to send shorter paging indicator bits to the mobile. The mobile monitors its designated paging indi- cators. If the paging indicators show that there is no mobile-specific page, then the mobile does nothing. If the paging indicators show that there is a mobile-specific page coming in, then the mobile wakes up and monitors its assigned paging channel slot. Note that in this regard, the F-QPCH works with a paging channel operating in slotted mode. In addition, the F-QPCH can also work with a forward common con- trol channel operating in slotted mode.
2.3.2.1 Paging Indicators
Figure 2.3 shows in more detail how the F-QPCH works in conjunction with the F-PCH. As one can see in the figure, a paging channel slot and a quick paging chan- nel slot both last 80 ms, and quick paging channel slots are offset from (ahead of) paging channel slots by 20 ms. Each quick paging channel is divided into four 20-ms portions. In this case, let’s assume that a mobile’s assigned paging channel slot is slot Y. Instead of always monitoring paging channel slot Y, the mobile would monitor
2.3 Signaling Channels 17
Paging channel slot (Y)
Quick paging channel slot (y)
Z 20-ms portion y2 y4 z2 z4 y1 y3 z1 z3 Y X p p p: Paging indicator 80-ms 80-ms
Figure 2.3 Channel format: F-QPCH. As an example, the figure shows two paging indicators located in the second and fourth 20-ms portions of the quick paging channel slot (y).
its paging indicators in the quick paging channel slot (y) that comes before the assigned paging channel slot (Y).
In a quick paging channel slot, the mobile always monitors two paging indica- tors. The two paging indicators either fall in the first 20-ms portion and in the third 20-ms portion (e.g., y1 and y3), or fall in the second 20-ms portion and in the fourth 20-ms portion (e.g., y2 and y4). So in our example, if two mobiles are both assigned paging channel slot Y, the first mobile may monitor a paging indicator in y1 and a paging indicator in y3; the second mobile may monitor a paging indicator in y2 and a paging indicator in y4. In actuality, the exact position of a paging indicator in the 20-ms portion is determined by a hash algorithm, the same type of algorithm that determines the assigned paging channel slot for a mobile operating in the slotted mode.
2.3.2.2 Other Indicators
In addition to carrying paging indicators, the F-QPCH also carries two other types of indicators: broadcast indicators and configuration change indicators. The mobile monitors its broadcast indicators to check if it needs to monitor its assigned slot (for broadcast messages) on the forward common control channel or paging channel. Furthermore, all mobiles monitor configuration change indicators; these indicators are used to inform mobiles of a change in configuration parameters (e.g., neighbor list) [2].
The relative positions of broadcast and configuration change indicators are shown in Figure 2.4. As shown in the figure, the number of broadcast and configura- tion change indicators depends on the data rate of the F-QPCH.
2.3.2.3 Characteristics of Quick Paging Channel
One distinguishing feature of the F-QPCH is that this physical channel has no error protection. This means that the bits sent on the F-QPCH do not have CRC bits
Quick paging channel slot (y)
20-ms portion y2 y4 z2 z4 y1 y3 z1 z3 bc bc bc bc b: Broadcast indicator
c: Configuration change indicator
b=4 and c=4 if F-QPCH data rate = 4.8 bpsK b=2 and c=2 if F-QPCH data rate = 2.4 bpsK 80-ms
added, are not convolutionally coded, and are not block-interleaved. The reason for this design choice is that paging indicator bits need to be quickly demodulated at the receiver so a decision can be made quickly regarding whether or not to monitor the paging channel slot that follows. Not needing to check the CRC bits, convolution- ally decode all the bits, and deinterleave save a lot of processing time. Note that this is the same reason for not error-protecting the power control bits in IS-95 (and in IS-2000). Power control bits need to be demodulated quickly so that power control decisions can be made quickly to adapt to changing channel conditions.
An IS-2000 carrier can have up to three quick paging channels. However, con- figuration change indicators and broadcast indicators are only used on the first quick paging channel [2].