EE360: Lecture 13 Outline Adaptive Techniques for Cellular Introduction Dynamic Channel and Resource Allocation Area Spectral Efficiency Adaptive Rate and Power “On the performance of adaptive modulation in cellular systems”: Taek Chung Adaptive CDMA “Optimal power control law for multimedia multirate CDMA systems”: Anne Aaron

Dynamic Channel Allocation Fixed channel assignments are inefficient Channels in unpopulated cells underutilized Handoff calls frequently dropped Channel Borrowing A cell may borrow free channels from neighboring cells Changes frequency reuse plan Channel Reservations Each cell reserves some channels for handoff calls Increases blocking of new calls, but fewer dropped calls Dynamic Channel Allocation Rearrange calls to pack in as many users as possible without violating reuse constraints Very high complexity “DCA is a 2G problem”

Dynamic Resource Allocation Cellular system performance is improved by dynamically allocating resources as user locations, bandwidth and QOS requirements, and applications change. BASE STATION Resources Power Rate Codes Channels Base Stations Access

Area Spectral Efficiency BASE STATION A=.25D2p = S/I increases with reuse distance. For BER fixed, tradeoff between reuse distance and link spectral efficiency (bps/Hz). Area Spectral Efficiency: Ae=SRi/(.25D2p) bps/Hz/Km2.

ASE with Adaptive Modulation Users adapt their rates (and powers) relative to S/I variation. S/I distribution for each user based on propagation and interference models. Computed for extreme interference conditions. Simulated for average interference conditions. The maximum rate Ri for each user in a cell is computed from its S/I distribution. For narrowband system use adaptive MQAM analysis

Propagation Model Two-slope path loss model: Slow fading model: log-normal shadowing Fast fading model: Nakagami-m Models Rayleigh and approximates Ricean. ASE maximized with reuse distance of one! Adaptive modulation compensate for interference

Average Area Spectral Efficiency ASE vs. Cell Radius fc=2 GHz 101 100 D=4R Average Area Spectral Efficiency [Bps/Hz/Km2] D=6R D=8R 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Cell Radius R [Km]

Variable Rate and Power Narrowband systems (Taek) Vary rate and power (and coding) Optimal power control not obvious CDMA systems (Anne) Multiple methods to vary rate (VBR, MC, VC) Optimization criteria Maximize throughput/capacity Meet different user requirements (rate, SIR, delay, etc.) Maximize revenue

Summary Adaptive techniques in cellular can improve significantly performance and capacity Finding an optimal adaptation strategy is complicated by interference from other cells Power control must balance link optimization with interference effects Most 2.5 and 3G systems use adaptation