Figure 19: The black hexagons in the graphic represent the geographical cells of a cellular network. Each cell contains a mobile tower at the center of the cell (towers T1, T2, T3, T4 in the illustration). Each tower transmits into its cell using three different frequencies in three different directions that are 120 degrees apart (shown by the blue double headed arrows). The actual cell in the cellular network is therefore the red colored hexagons in the graphic. Each of these red colored cells is divided into three regions (R1, R2, R3). Each cell tower services one region within a red cell. When the mobile phone M1 shown in the graphic is switched on, it will scan for signals from all neighboring towers. Since it lies in region R1 it will in theory find the strongest signal coming from tower T1 and begin communicating with it.

 

A cellular phone network enjoys several important advantages over the “zero-G” hub-and-spoke networks described in the previous chapter. Since each cell covers a geographically small area, much less power is needed to transmit and receive signals. This makes the cell phone batteries smaller and less heavy. This in turn reduces the overall size and weight of the mobile phone. Cellular networks also operate in the Ultra High Frequency (UHF) band leading to short stubby antenna designs on the phones instead of the out-sized antennae that were needed by the Very High Frequency (VHF) based car phone systems of the 1940s, 50s and 60s. The cellular nature of the network also means that the “over-the-horizon” issue faced by the zero-G networks is very elegantly avoided. A cellular network can scale virtually infinitely over and across mountains, around tall buildings, and across rivers and lakes simply by adding more cells to the network. Finally, and very importantly, on a cellular network two subscribers can talk on the same frequency band as long as they are in different cells. This enormously increases the number of simultaneous conversations that the network can support, and thereby addresses the network congestion problem that plagued the hub-and-spoke based zero-G networks.

 

Birth of cellular telephony concepts

 

The genesis of cellular telephony began as early as 1940s in Bell Labs, USA. However, cellular networking concepts continued to be researched upon all the way through to late 1970s, i.e. in parallel with the large scale roll outs of zero-G networks that were happening world wide as described in the previous chapter.

 

On 11 December 1947, Bell Labs researcher Douglas H. Ring together with his colleague W. Rae Young dispatched an internal Bell Labs technical memo that introduced the concept of utilizing adjacently located cellular coverage areas so as to increase the coverage of the mobile telephone service across the nation. While the memo was detailed enough in the description of how the cellular network would function in theory, the technology to actually make it work did not exist at the time. Neither had the Federal Communications Commission (FCC) in the United States opened out the frequency channels that such a cellular system would need. Given this situation, the field of cellular telephony would languish for another 20 years. Meanwhile, AT & T continued to petition the FCC for additional frequency allocations. Researchers at Bell Labs and Motorola as well as ones outside the United States would also continue to make progress in cellular telephony research.