Electronics & Telecommunications1 ENTC455 WIRELESS TRANSMISSION SYSTEMS ENTC 455

Electronics & Telecommunications2 ENTC455 Basics of Wireless Networks Harvey Lehpamer – Transmission Systems Design Handbook for Wireless Networks  Chapter 2 – pages 5 to 45

Electronics & Telecommunications3 ENTC455 Basics of Wireless Networks Historical Background – The Cellular Concept Wireless Local Loop (WLL) Cellular Systems  Analog (FDMA) – AMPS  Digital: TDMA: NA-TDMA (IS-136), GSM CDMA (IS-95)  1G, 2G, 2.5G, 3G,….. Satellite Networks Microwave Systems Bluetooth

Electronics & Telecommunications4 ENTC455 Historical Background 1946 – the first public mobile telephone service was introduced in 25 major American cities  Transmitter tower that serves a metropolitan area (> 50 km)  Mobile users  Several channels available Half-duplex mode 120 khz of bandwidth per channel (voice) 1960’s  Channels 30 Khz of bandwidth per channel (voice)  IMTS – Improved Mobile Telephone Service Full duplex, auto-dial, auto-trunking phone systems Spectrally innefficient  1976 – New York – 12 channels that could serve only 543 paying customers

Electronics & Telecommunications5 ENTC455 Cellular Concept (proposed in 1968, implemented late 70’s) Metropolitan areas were divided into cells Small geographic area: cells Low power transmitters Frequency re-use Each cells operating on a set of frequencies that differed from the frequencies of adjacent cells.

Electronics & Telecommunications6 ENTC455 Cellular Concept Figure 3: Mobile Telephone System Using a Cellular Architecture

Electronics & Telecommunications7 ENTC455 Cellular Concept – Frequency reuse Cell cluster Cluster Size N = 7 Frequency reuse factor = 1/7 Each cell contains one-seventh of the total number of available channels

Electronics & Telecommunications8 ENTC455 Frequency reuse concept A cell cluster is replicated over the coverage area

Electronics & Telecommunications9 ENTC455 Cellular Network Figure 8: Cellular System Components Mobile Switching Center Up Link Down Link

Electronics & Telecommunications10 ENTC455 Handoffs Figure 7: Handoff between Adjacent Cells

Electronics & Telecommunications11 ENTC455 Method of locating co-channel cells in a cellular system Number of cells per cluster N N can only have values that Satisfy the equation: N = i 2 + i j + j 2 To find the nearest co-channel neighbors of a particular cell: 1) move i cells along any chain of hexagons 2) turn 60 degrees counter-clockwise and move j cells N = 7 i = 2 j = 1

Electronics & Telecommunications12 ENTC455 Example – To understand how frequency re-use improves capacity If a total of 5 MHz of bandwidth is allocated to a particular FDD wireless system which uses 25 KHz simplex channels to provide full duplex voice and control channels, compute the number of channels available per metropolitan area. 25 KHz 5,000 KHz

Electronics & Telecommunications13 ENTC455 Solution Total bandwidth = 5 MHz Channel bandwidth = 25 KHz x 2 simplex channels = 50 KHz/duplex channel Total available channels = 5,000/50 = 100 channels 25 KHz 5,000 KHz Reverse ChannelForward Channel

Electronics & Telecommunications14 ENTC455 Now assume: Number of channels C =100 Traffic intensity generated by each user:  μ: call request rate: 2 calls/hour  H: Holding time: 3 minutes/call  Au = μ x H = 2 x (3/60) = 0.1 Erlangs Grade of Service: 1% Blocked calls cleared (Erlang-B formula) How many users can this system support?

Electronics & Telecommunications15 ENTC455 How many users? A = 84.1 Erlangs U = A / Au = 84.1 Erlangs / 0.1 Erlangs/user = = 841 users Number of channels CCapacity (Erlangs) for GOS=

Electronics & Telecommunications16 ENTC455 Example – Cellular System If a total of 5 MHz of bandwidth is allocated to a particular FDD cellular wireless system which uses 25 KHz simplex channels to provide full duplex voice and control channels, compute the number of channels available per cell if a system uses  4-cell reuse  7-cell reuse 25 KHz 5,000 KHz

Electronics & Telecommunications17 ENTC455 Solution Total bandwidth = 5 MHz Channel bandwidth = 25 KHz x 2 simplex channels = 50 KHz/duplex channel Total available channels = 5,000/50 = 100 channels A) for N=4  Total number of channels per cell = 100/4 = 25 channels B) for N=7  Total number of channels per cell = 100/7 ~14 channels

Electronics & Telecommunications18 ENTC455 For N=7: Number of channels per cell C =14 Traffic intensity generated by each user:  μ: call request rate: 2 calls/hour  H: Holding time: 3 minutes/call  Au = μ x H = 2 x (3/60) = 0.1 Erlangs Grade of Service: 1% Blocked calls cleared (Erlang-B formula) How many users per cell?

Electronics & Telecommunications19 ENTC455 For N=7: (cont.) From the Erlang B chart:  Total carried traffic A = 9 Erlangs  Number of users/cell U = A/ Au = 9/0.1 = 90 users  If there are 100 cells in a metropolitan area, then the total number of subscribers is  Exercise: Do the calculations for N=4

Electronics & Telecommunications20 ENTC455 Conclusion C = 100 channels Number of subscribers One antenna – no frequency re-use Cellular, N=7 Cellular, N=4 841 users 90 users/cell Homework: page 8, explain the numbers of second paragraph