Radio Frequency Channelization

NetPro Certification Courseware for NetPro Certified Telecom Engineer – N.C.T.E

Radio-Frequency Channelization Paired Channels There are a total of 832 channel pairs allocated per cellular market by the FCC. Since cellular is a duplex system like IMTS, two radio channels are needed for each cellular conversation. The channel transmitted from the base station t9 the subscriber's mobile phone is known as the forward channel or downlink. The channel transmitted from the mobile phone to the base station is known as the reverse channel or uplink Paired channels are the combination of the forward channel and the reverse channel that are necessary for every cellular conversation to take place. The two respective frequencies of the mobile transmit (base receive) and the base transmit (mobile receive) are combined to form the duplex channel that is used for every wireless call. See Figure. Note: Since the cellular industry is a duopoly each wireless carrier in every cellular market is allocated 416 channel pairs. 416 channels are used for the base transmit/mobile receive side, and 416 channels are used for the mobile transmit/base receive side. Most cellular carriers partition their 416 channel (pairs) into the N = 7 frequency-reuse format, the de facto industry standard. Other frequency reuse plans exist, but they are not widely used. Base station transmit and receive bands are separated by 45 MHz of spectrum to avoid interference between cellular radio transmit and receive channels.

Figure: Representation of downlink and uplink a paired channel.


Channel Spacing Channel spacing refers to the actual bandwidth space that is allocated for every cellular channel out of the total amount of cellular spectrum. In AMPS the channel spacing is 30 kHz. Every uplink and downlink each occupies 30 kHz of bandwidth. This means that every cellular call actually occupies a total of 60 kHz of cellular spectrum: 30 kHz for the forward channel and 30 kHz for the reverse channel. In other words, 30 kHz for the uplink, 30 kHz for the downlink. Each designated pair of frequencies-paired channel-that will be reused has been assigned a specific channel number under FCC guidelines and industry standards. This channel number equates directly to one specific paired channel, and its associated frequencies. See Table for a sample of how paired channels are assigned in the cellular industry, using the 30-kHz channel spacing standard. Control Channel The control channel, also called the paging channel, is a data signaling channel that handles the administrative overhead of the cellular system via messaging between mobile phones, cell base stations, and the MSC. It is used to administer the following tasks: TABLE FCC Base Station Base Station MobileMobile Channel Receive, Transmit Transmit, Receive No. MHz(Uplink) MHz(Downlink) MHz(Uplink) MHz(Downlink) 1 825.030 870.030 825.030 870.030 2 825.060 870.060 825.060 870.060 3 825.090 870.090 825.090 870.090 4 825.120 870.120 825.120 870.120 5 825.150 870.150 825.150 870.150 Figure: Sample of Paired Channels (A Band) and their FCC Numbers Setup of cellular calls, both mobile-originated and mobile-terminated. Locating (paging) cellular phones before connecting mobile-terminated calls. Collecting call information such as billing and traffic statistics. Autonomous mobile registration, i.e., registering phones on the system-both home and roaming" phones.


Of the 416 total channel pairs allocated per cellular carrier per market, 21 channel pairs are control channels. Like the 395 voice channels, the 21 control channels are also reused over and over again throughout cellular markets. All subscriber units-once they are powered on and throughout the time they are powered on-"tune" to the control channel in their assigned band (A or B band) from which they receive the strongest signal. Each subscriber unit automatically retunes the control channels in its band at predetermined intervals, based on system and carrier parameters. This interval can range from every 2 minutes to every 60 minutes'. When a subscriber pushes the "send" button when placing a call, the phone again rescans for the strongest control channel signal.

Channel Sets Each cell base station is assigned a particular number of cellular channels. This group of channels is known as a channel set. In an N = 7 frequency-reuse plan, there are 21 channel sets, with an average of 15 to 20 paired channels assigned per set. Channel sets are assigned on an alphanumeric basis. There are 21 channel sets because channel sets are assigned alphanumerically in groups of three, using the N = 7 reuse format. For example, there is channel set Al, A2, and A3. Then there is channel set Bi, B2, and B3; and so on. This alphanumeric configuration was developed by AT&T (Bell Labs). For example: Channel Set Numbers* (N=7) I A1 A2 A3

2 B1 B2 B3

3 C1 C2 C3

4 D1 D2 D3

5 E1 E2 E3

6 F1 F2 F3

7 G1 G2 G3

Each alphanumeric designation equals one channel set.


Figure: Channel sets and channel reuse (in association with N = 7 frequency-reuse plan). Channel sets are assigned in this manner up to the letter C, because G is the seventh letter of the alphabet and this equates to the N = 7 frequency-reuse formula. Seven cell clusters times 3 channel sets equals 21 total channel sets. See Figure for a depiction of 14 channel sets assigned in two N = 7 "clusters." Note: The terms frequency and channel are synonymous. Frequency reuse is synonymous with the term channel reuse because all frequencies in the cellular spectrum have been divided into discrete channels. See Table for a sample of several standard channel sets, using FCC channel numbers to illustrate frequency assignments for each channel set.


Signal (Control) Channels (One Control Channel per Channel Set) 333 312 291 270 249 228 207 186 165 144 123 102 81 60 39 18

332 311 290 269 248 227 206 185 164 143 122 101 80 59 38 17

331 310 289 268 247 226 205 184 163 142 121 100 79 58 37 16

330 309 288 267 246 225 204 183 162 141 120 99 78 57 36 15

329 308 287 266 245 224 203 182 161 140 119 98 77 56 35 14

328 307 286 265 244 223 202 181 160 139 118 97 76 55 34 13

327 306 285 264 243 222 201 180 159 138 117 96 75 54 33 12

326 305 284 263 242 221 200 179 158 137 116 95 74 53 32 11

325 304 283 262 241 220 199 178 157 136 115 94 73 52 31 10

1015 914 706 685 664

1014 913 705 684 663

1013 912 704 683 662

1012 911 703 682 661

Extended Channels (Expanded Spectrum) 1020 919 711 690 669

1019 918 710 689 668

1018 917 709 688 667

1017 916 708 687 666

1016 915 707 686 665

* Each 3<1igit number represents a channel pair.

Radio Frequency Channelization

Recommend Documents