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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"><!--Converted with LaTeX2HTML 96.1 (Feb 5, 1996) by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds --><HTML><HEAD><TITLE>Channels</TITLE><META NAME="description" CONTENT="Channels"><META NAME="keywords" CONTENT="gprs"><META NAME="resource-type" CONTENT="document"><META NAME="distribution" CONTENT="global"><LINK REL=STYLESHEET HREF="gprs.css"></HEAD><BODY LANG="EN"> <A NAME="tex2html156" HREF="node5.html"><IMG WIDTH=37 HEIGHT=24 ALIGN=BOTTOM ALT="next" SRC="http://cbl.leeds.ac.uk/nikos/figs/next_motif.gif"></A> <A NAME="tex2html154" HREF="node3.html"><IMG WIDTH=26 HEIGHT=24 ALIGN=BOTTOM ALT="up" SRC="http://cbl.leeds.ac.uk/nikos/figs/up_motif.gif"></A> <A NAME="tex2html148" HREF="node3.html"><IMG WIDTH=63 HEIGHT=24 ALIGN=BOTTOM ALT="previous" SRC="http://cbl.leeds.ac.uk/nikos/figs/previous_motif.gif"></A> <BR><B> Next:</B> <A NAME="tex2html157" HREF="node5.html">TDMA Slot Structure</A><B>Up:</B> <A NAME="tex2html155" HREF="node3.html">MAC Implementation Details</A><B> Previous:</B> <A NAME="tex2html149" HREF="node3.html">MAC Implementation Details</A><BR> <P><H2><A NAME="SECTION00121000000000000000">Channels</A></H2><P>The physical air interface provided by <I>ns</I> is used. The number offrequency channels to be created for the Uplink and Downlink can be set bythe user through <EM>max_num_freq</EM> in the OTcl script. We differentiatebetween the uplink and downlink channels by creating separate timers toclock the TDMA on each. A hard-coded skew of 3 time-slots is maintainedbetween the uplink and downlink TDMA frames. On each frequency (uplink aswell as downlink), slot 0 is reserved for signalling and broadcasts. Theuser can decide the number of slots to reserve for GPRS traffic on eachfrequency through <EM>gprs_slots_per_frame</EM> in the OTcl script. Theremaining slots are left for GSM mobiles. The frequency channel a packetis to be transmitted on is stamped onto a new field called <EM>chan_</EM> inthe common header of the packet.<P>The logical channels are mapped such that:<P>PBCH - slot0 on uplink/downlink frequency 0.<P>PRACH - slot0 on uplink frequency 0.<P>PAGCH - slot0 on downlink frequency 0.<P>PDTCH - all other slots/frequencies.<P><BR> <HR><P><ADDRESS><I>Richa Jain (96D07007) <BR>Tue Jul 24 22:29:53 IST 2001</I></ADDRESS></BODY></HTML>?? 快捷鍵說明
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