How to Broadcast Multimedia Contents?
[Note] Due to the asymmetry between the uplinks and downlinks of a mobile network, there are different considerations, tradeoffs and techniques for designing each directions. In general, with the recent advance on uplink interference cancellation and management techniques, mobile network is usually limited by downlinks due inter-cell interference, especially when delay is a key part of the equation. On this blog, my focus will be on downlinks. How to evolve mobile system uplinks will be discussed in separated blogs.
Mobile system design usually starts from our understanding of wireless channels and the services customers are demanding. The properties of various wireless channels can help us understand the system design limitation we are facing and the potentials we may achieve. For example, COST 231 model, which was developed by European COST Action 231. Its variations are the most popular radio propagation models used in almost every wireless standardization body, including 3GPP, 3GPP2 and IEEE. Its modifications include COST 231-Hata Model and COST 231-Walfisch-Ikegami Model. One nice thing of COST 231 channel model is it helps us understand the tradeoff between reception and coverage we are facing in a typical single-cell environment.
|Figure 1. Spectral Efficiency and Coverage Tradeoff|
As shown in Figure 1, with a 300-meter-tall transmitter antenna, we can see that the path-loss changes 0.66 dB at every 90% coverage change, 1.39 dB at every 80% coverage change, 2.22 dB at every 70% coverage change and 3.18 dB at every 60% coverage change. In general, if you want more coverage, then you may lose some capacity especially on the cell-edge. Otherwise, you have to shrink your coverage.
|Figure 2. What we want to achieve.|
|Figure 3. Mobile System Design Options|