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CHAPTER III - Improving Performance to Keep Up with Demand

Expanding network capacity to meet the ever-growing demand for wireless connectivity is an ongoing challenge. But just as a number of factors have been responsible for increasing mobile traffic, a number of technical developments have been responsible for expanding network capacity to keep pace with demand.

Fortunately, progress in improving performance of wireless communication has been steady and reliable. Martin Cooper, the inventor of the first mobile phone, having observed that the efficiency of wireless communication had been increasing at a constant rate since Marconi’s discovery of radio transmission in 1895, promulgated Cooper’s Law:

The maximum number of voice conversations or equivalent data transactions that can be conducted in all of the useful radio spectrum over a given area doubles every 30 months.1

Like Moore’s Law, Cooper’s Law is not a law of nature. Continuous improvement in wireless performance does not happen automatically; it is the result of large investments in research and development of new techniques and technologies. The million-fold improvement in spectrum use that has been realized over the past 45 years is based on three main factors: making use of more spectrum, enhancing modulation techniques and (especially) reducing the size of cells. Let’s consider each of these:

  • Increasing spectrum allocation. One obvious way to meet a growing demand is to increase the amount of spectrum available for this purpose. Finding more spectrum for wireless broadband communications has become a high priority globally. But the spectrum is a finite resource and the most desirable portions of the spectrum have already been allocated and are mostly in use, either by the government or by commercial users for many purposes including mobile communications.

Over the past two decades, the FCC has conducted auctions as a means of increasing spectrum available for wireless communications, but costs are going up. The AWS-3 auction for 65 MHz of spectrum, which ended in January 2015, attracted $44.9 billion in bids, far in excess of the pre-auction estimates of $10 to $20 billion.

  • Improving modulation schemes. Engineers have developed a variety of techniques, including time division multiplexing and frequency division multiplexing, to cram more data into a given amount of spectrum. For example, the introduction of OFDM (orthogonal frequency-division multiplexing) in LTE, the current 4G standard, resulted in a very large reduction in the cost per bit per second for data transmission compared with the previous 3G standard. Modulation schemes can also provide significant reductions in latency (delay), which is critical for certain applications.
  • Reducing cell size. Shrinking cell size makes it possible to accommodate many more users in the same geographic area and also to improve wireless performance. Over the past several decades, the maximum size of cells has shrunk from a radius of five miles under the 1G standard to just 300 yards under the current 4G standard. Cell size will continue to shrink as we move from macrocells to microcells and from microcells to picocells and femtocells that cover a single room or even a portion of a room.

The cost of smaller cells has fallen as has the cost of backhaul (routing wireless traffic to land lines for access to the “core” network) on a per bit basis. However, the civil engineering work involved with installing cells is not declining as cell size decreases and the density of cells increases. In addition, the challenge of providing sufficient backhaul capacity managing wireless networks with ever-larger numbers of smaller cells is substantial.

An online discussion of Cooper’s Law noted that each of these three factors has contributed to the realization of the million-fold improvement in the way we use spectrum over the past half century: the availability of more spectrum was responsible for about a 25-times increase; better modulation techniques contributed to another 25-times improvement; and the ability to re-use spectrum by shrinking cell size resulted in a 1600-fold improvement in efficiency.

1 Martin Cooper, “Antennas Get Smart,” Scientific American, July 1, 2003.

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