Wednesday, August 26, 2015

Wireless vs. Wireline

Wireless technology is playing a profound role in networking and communications, even though wireline technologies such as fiber have inherent capacity advantages. Relative to wireless networks, wireline networks have had greater capacity and historically have delivered faster throughput rates.

While wireless networks can provide a largely equivalent broadband experience for many applications, for ones that are extremely data intensive, wireline connections will remain a better choice for the foreseeable future. For example, users streaming Netflix movies in high definition consume about 5 Mbps. Typical LTE deployments use 10 MHz radio channels on the downlink and have a spectral efficiency of 1.4 bps/Hertz (Hz), providing LTE an average sector capacity of 14 Mbps. Thus, just three Netflix viewers could exceed sector capacity. In the United States, there are approximately 1,100 subscribers, on average, per cell site8, hence about 360 for each of the three sectors commonly deployed in a cell site. 

In dense urban deployments, the number of subscribers can be significantly higher. Therefore, just a small percentage of subscribers can overwhelm network capacity. For Blu-ray video quality that operates at around 16 Mbps or Netflix 4K streaming that runs at 15.6 Mbps, an LTE cell sector could support only one user.

Even if mobile users are not streaming full-length movies in high definition, video is finding its way into many applications, including education, social networking, video conferencing, business collaboration, field service, and telemedicine.

Over time, wireless networks will gain substantial additional capacity through  the methods discussed in the next section, but they will never catch up to wireline. One can understand this from a relatively simplistic physics analysis:
q  Wireline access to the premises or to nearby nodes uses fiber-optic cable.
q  Capacity is based on available bandwidth of electromagnetic radiation. The infra- red frequencies used in fiber-optic communications have far greater bandwidth than radio.
q  The result is that just one fiber-optic strand has greater bandwidth than the entire usable radio spectrum to 100 GHz, as illustrated in Figure 1.

Figure 1: RF Capacity vs. Fiber-Optic Cable Capacity
A dilemma of mobile broadband is that it can provide a broadband experience similar to wireline, but it cannot do so for all subscribers in a coverage area at the same time. Hence, operators must carefully manage capacity, demand, policies, pricing plans, and user expectations. Similarly, application developers must become more conscious of the inherent constraints of wireless networks.

Mobile broadband networks are best thought of as providing access to higher-capacity wireline networks. The key to improving per-subscriber performance and bandwidth is reducing the size of cells and minimizing the radio path to the wireline network, thus improving signal quality and decreasing the number of people active in each cell. These are the motivations for Wi-Fi offload and small-cell architectures.

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