Cellular Networks No. 1  Seattle Pacific University Cellular Wireless Networks Common issues for wireless solutions Kevin Bolding Electrical Engineering Seattle Pacific University

Cellular Networks No. 2  Seattle Pacific University Wireless Systems H Base Network Handsets – Portable mobile devicesBase Station - Receiver Network connects base stations

Cellular Networks No. 3  Seattle Pacific University Generic Cellular System H Base H H H H H H H H H H H H H H H H H H H Base Station Controller Mobile Switching Center PSTN

Cellular Networks No. 4  Seattle Pacific University Basic Issues for Mobile Communications H Base How do we manage multiple handsets communicating with one base? HHHH Base H How do we manage handsets entering and leaving communication? Base H How do we manage handsets moving from base station to base station? Base

Cellular Networks No. 5  Seattle Pacific University Basic Issues for Mobile Communications How do we manage multiple handsets communicating with one base? H Base H H H H Multiplexing (sharing the channel) Analog - Frequency-division Digital - Frequency-division and Time-division (GSM) Code-division (CDMA) We need at least: 1 send channel for each mobile 1 receive channel for each mobile 1 control channel

Cellular Networks No. 6  Seattle Pacific University Basic Issues for Mobile Communications Base H How do we manage handsets entering and leaving communication? To initiate a call Mobile issues request on paging channel Receiving towers “discuss” who will answer To receive a call System must know where the mobile is Idle mobile periodically broadcasts on paging channel System broadcasts page signal on paging channel for all bases near mobile

Cellular Networks No. 7  Seattle Pacific University Basic Issues for Mobile Communications Base H How do we manage handsets moving from base station to base station? Base Mobile uses idle slots to monitor control channels of nearby bases Keeps sorted list of the most powerful ones If error rate increases, mobile can either Increase power on same channel, same base Switch to a new base Handoff from base to base managed at higher level May be a soft handoff

Cellular Networks No. 8  Seattle Pacific University Cells Circles don’t tile well… Ideally, each base station serves a circular area Use Hexagons as approximations

Cellular Networks No. 9  Seattle Pacific University Cell Channel Assignment Patterns We need to organize patterns for assigning channels to cells Form a basic cell cluster that will be repeated (tiled) to cover the entire service area Each cell in a cluster is assigned a different set of channels More cells in cluster  Fewer channels per cell R = Cell radius D R D = Distance between co-channel neighbors Basic criterion – adjacent cells never have the same channel group Keep cells with the same channel group as far apart as possible Use D/R ratio (Larger is better) Secondary criterion – adjacent cells have channels at least two channel groups apart Channel 3 not adjacent to channels 2 or 4, etc.

Cellular Networks No. 10  Seattle Pacific University C/I is Carrier-to-Interference Ratio AMPS modulation characteristics require  18 dB co-channel C/I over single interferer Between a pair of sites using same channel, three C/I regions exist: Site A C/I better than 18 dB Neither site gives usable C/I Site B C/I better than 18 dB Co-Channel Interference Model D R Need a D/R that provides 18+dB C/I D/R > 4 generally works

Cellular Networks No. 11  Seattle Pacific University Cell Arrangement as a Function of N N=1 Lethal, works well in CDMA Awful C/I: Every neighbor is co- channel Every neighbor cell is adjacent channel too! Center 1/3 of each cell OK, rest is lost in horrible interference N=2 Better, but still lethal Each cell still has 2 co-channel neighbors Each cell has 4 adjacent channel neighbors

Cellular Networks No. 12  Seattle Pacific University N = 3 Better, but still lethal Co-channel neighbors are now spaced at D/R of better, but not 18 dB.... Each cell has 6 adjacent channel neighbors - all neighbors are adjacent!! Cell Arrangement as a Function of N N = 4 Better, but still lethal Co-channel neighbors are now spaced at D/R of Each cell has 4 adjacent channel neighbors R D

Cellular Networks No. 13  Seattle Pacific University N = 5 Better, but not good enough Co-channel neighbors farther away 2 at D/R of at D/R of 4.58 Some cells have 2 adjacent channel neighbors, some have 3 Cell Arrangement as a Function of N N = 6 Better, but not by much Co-channel neighbors farther away 2 at D/R of at D/R of at D/R of 6.0 Some cells have 2 adjacent channel neighbors, some have 3

Cellular Networks No. 14  Seattle Pacific University N = 7 First arrangement that works in most propagation environments, giving 18+ dB C/I Co-channel neighbors farther away 6 at D/R of 4.58 Each cell always has 2 adjacent channel neighbors Cell Arrangement as a Function of N N = 8 Better, but not worthwhile Co-channel neighbors farther away 4 at D/R of at D/R of at D/R of 6.93 Of the eight cells in the cluster, 2 have 2 adjacent-channel neighbors and 4 have 1 adjacent channel neighbor

Cellular Networks No. 15  Seattle Pacific University N = 9 Significant improvement Co-channel neighbors farther away 6 at D/R of 5.20 Out of 9 cells in cluster, 4 have 1 adjacent channel neighbor and 3 have 2 such neighbors Cell Arrangement as a Function of N N = 10 Not impressively better Co-channel neighbors farther away 2 at D/R of at D/R of at D/R of 6.06 Out of 10 cells in cluster, 6 have 1 adjacent channel neighbor 3 have 2 adjacent-channel neighbors

Cellular Networks No. 16  Seattle Pacific University N = 11 Slightly better Co-channel neighbors farther away 2 at D/R of at D/R of at D/R of 7.14 Out of 11 cells in cluster, eight each have one adjacent channel neighbor Cell Arrangement as a Function of N N = 12 Excellent but inefficient Co-channel neighbors farther away 6 at D/R of 6.0 No adjacent-channel neighbors

Cellular Networks No. 17  Seattle Pacific University Frequency Reuse Implications of N N is number of cells in frequency reuse pattern and is critically important since it determines: Capacity of an individual cell Channels per cell = (total channels) / N As N goes up, capacity progressively decreases Interference As N goes up, interference becomes progressively less troublesome Channels per Cell* Min D/R N * Assumes use of 395 voice channels including expanded spectrum

Cellular Networks No. 18  Seattle Pacific University Signal-to-Interference Ratios Signal-to-Interference (Also known as Carrier-to-Interference) Ratio: S/I = Signal Power / Interference Power Signal-to-Noise+Interference (Or just Signal-to-Noise) Ratio: S/(I+N) = Signal Power / (Interference Power + Noise Power) In a cellular system, the main source of interference is Co-channel Inteference (CCI) For any regular hex tiling pattern, there are 6 co-channel neighbors. CCI (total) = 6 x (CCI from individual interferer)

Cellular Networks No. 19  Seattle Pacific University Sector Cell Cluster – Frequency Reuse B1 B2 B3 C1 C2 C3 G1 G2 G3 A1 A2 A3 D1 D2 D3 E1 E2 E3 F1 F2 F3 120 degree sector F1 F2 F3 Gain Pattern of 120-degree sector antenna Directional sector antennas reduce the required D/R ratio

Cellular Networks No. 20  Seattle Pacific University Sectoring Reduces the Interference Only 2 of the 6 co-channels interfere now A 1C 1B 1A 1C 1B 1A 1C 1B 1A 1C 1B 1A 1C 1B 1A 1C 1B 1A 1C 1B Reduces CCI to 1/3 the previous level (reduced by 4.77dB)