Lee, WCY, Ziemer, R.E., Ovan, M. Mandyam, G.D. "Personal and Office The Electrical Engineering Handbook Ed. Richard C. Dorf Boca raton crc Press llc. 2000
Lee, W.C.Y., Ziemer, R.E., Ovan, M. Mandyam, G.D. “Personal and Office” The Electrical Engineering Handbook Ed. Richard C. Dorf Boca Raton: CRC Press LLC, 2000
75 Personal and office The Difference between Fixed- to- Fixed Radio Communication Mobile communication Natural problems in mobile rad Communications. Description of Mobile Radio Systems Data Systems. Personal Communication Service Systems 75.2 Facsimile William C. Y. Lee Scanning. Encoding. Modulation and Transmission Demodulation and Decoding. Recording. Personal Computer Facsimile.Group 4 Facsimile odger E. Ziemer 75.3 Wireless Local-Area Networks for the 1990s University of Colorado at Colorado The Wireless In-Building Vision. Market Research. LANMarket Factors. Cabling Problems. User Requirements Environment Mil Ovan Product Requirements: End User Reaction. Technology 75.4 Wireless PCs Giridhar D. Mandyam Cellular Band Systems. PCS Services.3rd Generation Nokia Research Center Enhancements 75.1 Mobile radio and Cellular Communications William C.y lee The Difference between fixed-to-Fixed Radio communication and Mobile communication In fixed-to-fixed radio communications, the transmitter power, antenna location, antenna height, and antenna gain can be determined after calculating the link budget. Also, depending on the frequency range of the carrier affected on the atmospheric variation, different"margin values will be put in the budget calculation for different system applications. The fixed-to-fixed radio links are usually 10 miles or longer and high above the ground The signal variation over the link is due mostly to atmospheric changes. Satellite communications, microwave links, troposcatter, etc are fixed-to-fixed radio communications. In mobile radio communications, the param eters such as transmitter power, antenna location, antenna height, and antenna gain are determined by covering suburban areas are less than 10 miles. In mobile radio communications, the design of cell coverage is baser d an area or cell In mobile radio communications at least one end is in motion the sizes of cells in urban he average power. No margin is applied in calculating the cell coverage. Natural Problems in mobile radio Communications In mobile radio communications, there are many problems which never occur in fixed-to-fixed radio commu 1. Excessive pathloss: Vehicles are referred to as mobile units. The antenna height of the mobile unit is very close to the ground. Therefore, the average signal strength received at the mobile unit has two components, c 2000 by CRC Press LLC
© 2000 by CRC Press LLC 75 Personal and Office 75.1 Mobile Radio and Cellular Communications The Difference between Fixed-to-Fixed Radio Communication and Mobile Communication • Natural Problems in Mobile Radio Communications • Description of Mobile Radio Systems • Mobile Data Systems • Personal Communication Service Systems 75.2 Facsimile Scanning • Encoding • Modulation and Transmission • Demodulation and Decoding • Recording • Personal Computer Facsimile • Group 4 Facsimile 75.3 Wireless Local-Area Networks for the 1990s The Wireless In-Building Vision • Market Research • LANMarket Factors • Cabling Problems • User Requirements Environment • Product Requirements: End User Reaction • Technology Alternatives in Meeting Customer Requirements 75.4 Wireless PCS Cellular Band Systems • PCS Services • 3rd Generation Enhancements 75.1 Mobile Radio and Cellular Communications William C. Y. Lee The Difference between Fixed-to-Fixed Radio Communication and Mobile Communication In fixed-to-fixed radio communications, the transmitter power, antenna location, antenna height, and antenna gain can be determined after calculating the link budget. Also, depending on the frequency range of the carrier affected on the atmospheric variation, different “margin” values will be put in the budget calculation for different system applications. The fixed-to-fixed radio links are usually 10 miles or longer and high above the ground. The signal variation over the link is due mostly to atmospheric changes. Satellite communications, microwave links, troposcatter, etc. are fixed-to-fixed radio communications. In mobile radio communications, the parameters such as transmitter power, antenna location, antenna height, and antenna gain are determined by covering an area or cell. In mobile radio communications, at least one end is in motion. The sizes of cells in urban and suburban areas are less than 10 miles. In mobile radio communications, the design of cell coverage is based on the average power. No margin is applied in calculating the cell coverage. Natural Problems in Mobile Radio Communications In mobile radio communications, there are many problems which never occur in fixed-to-fixed radio communication system: 1. Excessive pathloss: Vehicles are referred to as mobile units. The antenna height of the mobile unit is very close to the ground. Therefore, the average signal strength received at the mobile unit has two components, William C. Y. Lee AirTouch Communications, Inc. Rodger E. Ziemer University of Colorado at Colorado Springs Mil Ovan Motorola, Inc. Giridhar D. Mandyam Nokia Research Center
a direct wave and a ground-reflected wave. These two waves act in canceling their average signal strengths and result in excessive pathloss at the receiver 2. Multipath fading: Due to the human-made environment in which mobile units travel, the instantaneous ignal sent from the base station is reflected back and forth from buildings and other ground before arriving at the mobile unit and causes signal fading received in the time domain. This fading causes an increase in the bit error rate(BEr) and in the degradation of voice quality 3. Human-made noise: The antenna height of mobile units is usually low. Therefore, human-made industrial noise, automotive ignition noise, etc. are very easily received by the mobile unit. This noise will raise the noise floor and impact system perfor Ima 4. Dispersive medium: Due to the human-made environment and the low antenna height of the unit,the signal after bouncing back and forth from the human-made structures produces multiple reflected waves which arrive at the mobile unit at different times. One impulse sent from the base station propagating through the medium becomes multiple reflected impulses received at different times at the mobile unit. This medium is called a dispersive medium. First the dispersive medium does not affect the analog voice channel, but does affect the data channels. Second, the medium becomes effective depending on the transmission symbol rate of the system. The dispersive medium will impact the reception performance when the transmission rate is over 20 kbps. Third, the dispersive medium becomes more effective in urban areas than in suburban areas Description of Mobile Radio Systems There are two basic systems: trunked systems and cellular systems Trunked Systems A trunked system is assigned a channel from a number of available channels to a user. The user is never assigned to a fixed channel 1. Specialized mobile radio(SMR) is a trunked system. The SMR operator is licensed by the FCC to a group of 10 or 20 channels within 14 MHz of the spectrum between 800 and 900 MHz Loading requirement: A minimum of 70 mobile units per channel is required. SMR can offer privacy, channel access, and efficient services. It can serve up to 125-150 mobile units per channel. pacing: 25 kHz. Channel allocation: The FCC allocates a spectrum of either 500 kHz or 1 MHz to a SMr operator who will serve 10 or 20 paired transmit-receiver voice channels Coverage: Coverage is about 25 miles in radius since SMR uses only one high-power transmitting tower covering a large area. Telephone interconnect: The public service telephone network(PSTN) extends mobile telephone service to smr users Roaming: Mobile units are equipped with software that allows the radio to roam to any SmR syster in the network. Handoff: No tower-to-tower handoff capability; the channel frequency does not change as the unit moves from one cell to another ESMR(enhanced SMR): A system used to enhance the SMR system. It was called MIRS(Mobile Integrated Radio Systems). Now it is called IDEN (Integrated Dispatch and Enhanced Network). Features are: Uses the smr band Uses TDMA(time division multiple access)digital technology, the same digital TDMA standard adopted by the cellular Applies network of low-power cells Provides cell-to-cell handoffs through a centralized switching facility A spectrum average of 7-8 MHz is used in each market. The spectrum is not contiguous A channel bandwidth of 25 kHz is specified with three time slots per channel. Modulation 16 QAM is applied c 2000 by CRC Press LLC
© 2000 by CRC Press LLC a direct wave and a ground-reflected wave. These two waves act in canceling their average signal strengths and result in excessive pathloss at the receiver. 2. Multipath fading: Due to the human-made environment in which mobile units travel, the instantaneous signal sent from the base station is reflected back and forth from buildings and other ground objects before arriving at the mobile unit and causes signal fading received in the time domain. This signal fading causes an increase in the bit error rate (BER) and in the degradation of voice quality. 3. Human-made noise: The antenna height of mobile units is usually low. Therefore, human-made industrial noise, automotive ignition noise, etc. are very easily received by the mobile unit. This noise will raise the noise floor and impact system performance. 4. Dispersive medium: Due to the human-made environment and the low antenna height of the mobile unit, the signal after bouncing back and forth from the human-made structures produces multiple reflected waves which arrive at the mobile unit at different times. One impulse sent from the base station propagating through the medium becomes multiple reflected impulses received at different times at the mobile unit. This medium is called a dispersive medium. First the dispersive medium does not affect the analog voice channel, but does affect the data channels. Second, the medium becomes effective depending on the transmission symbol rate of the system. The dispersive medium will impact the reception performance when the transmission rate is over 20 kbps. Third, the dispersive medium becomes more effective in urban areas than in suburban areas. Description of Mobile Radio Systems There are two basic systems: trunked systems and cellular systems. Trunked Systems A trunked system is assigned a channel from a number of available channels to a user. The user is never assigned to a fixed channel. 1. Specialized mobile radio (SMR) is a trunked system. The SMR operator is licensed by the FCC to a group of 10 or 20 channels within 14 MHz of the spectrum between 800 and 900 MHz. • Loading requirement: A minimum of 70 mobile units per channel is required. SMR can offer privacy, speedier channel access, and efficient services. It can serve up to 125–150 mobile units per channel. • Channel spacing: 25 kHz. • Channel allocation: The FCC allocates a spectrum of either 500 kHz or 1 MHz to a SMR operator who will serve 10 or 20 paired transmit-receiver voice channels. • Coverage: Coverage is about 25 miles in radius since SMR uses only one high-power transmitting tower covering a large area. • Telephone interconnect: The public service telephone network (PSTN) extends mobile telephone service to SMR users. • Roaming: Mobile units are equipped with software that allows the radio to roam to any SMR system in the network. • Handoff: No tower-to-tower handoff capability; the channel frequency does not change as the unit moves from one cell to another. 2. ESMR (enhanced SMR): A system used to enhance the SMR system. It was called MIRS (Mobile Integrated Radio Systems). Now it is called IDEN (Integrated Dispatch and Enhanced Network). Features are: • Uses the SMR band. • Uses TDMA (time division multiple access) digital technology, the same digital TDMA standard adopted by the cellular industry. • Applies network of low-power cells. • Provides cell-to-cell handoffs through a centralized switching facility. • A spectrum average of 7–8 MHz is used in each market. The spectrum is not contiguous. • A channel bandwidth of 25 kHz is specified with three time slots per channel. • Modulation 16 QAM is applied. • No equalizer is used
(a)K=7 Ds/R'= 4.6 mearQ' (c)K=3 R·=R FIGURE 75.1 Four cases of expression of cochannel interference reduction factor Cellular Systems The cellular system [Lee, 1989]is a high-capacity system that uses the frequency reuse concept. The same frequency is used over and over again in different geographical locations. In large cities, the same frequency can be reused over 30 times Key Elements: There are several key elements in the cellular system. Cochannel interference reduction factor q(see Fig 75.1): Two cells using the same frequency channels are called cochannel cells. The required distance between two cochannel cells in order to receive the accepted voice quality is D, and the radius of the cell is R. Then the cochannel interference reduction factor q is q=D,/R There are six co-channel cells at the first tier seen from the center cell as shown in Fig. 75. 1(a). For an analog cellular system g, =4.6, and the cell reuse factor Kis K=9, 23=7. The K=7 means that a cluster of seven cells will reuse again and again in a serving area. The capacity increase in a cellular system can be achieved by reducing both the radius of cell r by one half and the separation D, by one half such at the gs remains constant and the capacity is increasing by four times. The reason is that a cell shown in Figure 75. 1(a)can fit in four small cells shown in Fig. 75.1(b). In Fig. 75.1(c), the size of cells is the same as Fig. 75.1(a),but , =3 is achieved by using an intelligent microcell system. The capacity of Fig. 75. 1(c)is 7= 2. 33 times over that of Fig. 75.1(a). In Fig. 75. 1(d), the radius of the cell is reduced by one half, and K is reduced to 3. The capacity of Fig. 75.1(d)is 4x 2.33=9.32 times over that of 751(a) The value of q is different in different kinds of cellular systems such as analog, TDMA, and CDMA(code Handoff: Handoff is a feature implemented in cellular systems to handoff a frequency of a cell while the mobile unit changes to another frequency of another cell while the vehicle is entering. The handoff is handled by the system and the user does not notice the handoff occurrences c 2000 by CRC Press LLC
© 2000 by CRC Press LLC Cellular Systems The cellular system [Lee, 1989] is a high-capacity system that uses the frequency reuse concept. The same frequency is used over and over again in different geographical locations. In large cities, the same frequency can be reused over 30 times. Key Elements: There are several key elements in the cellular system. • Cochannel interference reduction factor q (see Fig. 75.1): Two cells using the same frequency channels are called cochannel cells. The required distance between two cochannel cells in order to receive the accepted voice quality is Ds , and the radius of the cell is R. Then the cochannel interference reduction factor q is q = Ds/R There are six co-channel cells at the first tier seen from the center cell as shown in Fig. 75.1(a). For an analog cellular system qs = 4.6, and the cell reuse factor K is K = qs⅔ = 7. The K = 7 means that a cluster of seven cells will reuse again and again in a serving area. The capacity increase in a cellular system can be achieved by reducing both the radius of cell R by one half and the separation Ds by one half such that the qs remains constant and the capacity is increasing by four times. The reason is that a cell shown in Figure 75.1(a) can fit in four small cells shown in Fig. 75.1(b). In Fig. 75.1(c), the size of cells is the same as Fig. 75.1(a), but qs = 3 is achieved by using an intelligent microcell system. The capacity of Fig. 75.1(c) is ⁄ = 2.33 times over that of Fig. 75.1(a). In Fig. 75.1(d), the radius of the cell is reduced by one half, and K is reduced to 3. The capacity of Fig. 75.1(d) is 4 ¥ 2.33 = 9.32 times over that of Fig. 75.1(a). The value of q is different in different kinds of cellular systems such as analog, TDMA, and CDMA (code division multiple access). • Handoff: Handoff is a feature implemented in cellular systems to handoff a frequency of a cell while the mobile unit changes to another frequency of another cell while the vehicle is entering. The handoff is handled by the system and the user does not notice the handoff occurrences. FIGURE 75.1 Four cases of expression of cochannel interference reduction factor
TABLE 75.1 Specifications of TDMA and CDMA Systems TDMA CDMA Bandwidth per channel 1.23 MHz Time slots Speech coder 8 kbps(max )a variable rate vocoder Modulation T/4-DQPSK Forward radio channels Pilot(1)sync(1), Paging(7) 8 kbps-VSELP code traffic channels(55), total 64 vector sum excited LPC) channels Channel coding ate 1/2 convolutional(13 kbps) Reverse radio channels (9), traffic channels (55) Total transmit rate 48 kbps per channel Power control rd, reverse Diversity LPC linear predictive code. Cell splitting: When a cell provides a maximum of 60 radio channels and all are used during bus hours, the cell has to be split into smaller cells in order to provide more radio channels, normally reducing by four subcells. Each subcell 60 channels. The total area of an original cell will provide 240 radio channels which is four times higher Spectrum Allocation in the United States, Europe, and Japan: In the United States there is 50 MHz of ectrum allocated to cellular radio within 800-900 MHz. Based on duopoly, each city has two licensed operators. Each one operates on a 25-MHz band. There are two bands, Band A and Band B. Each band consists of 416 channels. The channel bandwidth is 30 kHz. Among 416 channels, 21 channels are used for setting up and 395 are used for voice channels Analog: The frequency management of both Band A and Band B is shown in Table 75.5. Digital: There are two potential systems, TDMA and CDMA shown in Table 75.1 In Europe the spectrum allocation is as shown in Table 75.2 and 75.3 In Japan the spectrum allocation is as shown in Table 75.4 TABLE 75.2 Specification of Three European Systems TACS NMT* Transmission frequency(kHz) Base statio 935960 463-467.5 461.3-465.74 Mobile station 890-915 453-457.5 451.3-455.74 Spacing between transmission Spacing between channels(kHz)25 Number of channels 0 30 Type of modulation 4 Type of modulation FSK ±6.4 ±3.5 ±25 Data transmission rate(kbps) 8 .28 essage protection lesage is sent again decision is employed when an error g to the is detected ontent of the s TACS=total access cellular system; NMT = nordic mobile telephone c2000 by CRC Press LLC
© 2000 by CRC Press LLC • Cell splitting: When a cell provides a maximum of 60 radio channels and all are used during busy hours, the cell has to be split into smaller cells in order to provide more radio channels, normally reducing the cell by using a half radius. As a result a cell will be covered by four subcells. Each subcell provides 60 channels. The total area of an original cell will provide 240 radio channels which is four times higher in capacity as compared with the original cell capacity before splitting. Spectrum Allocation in the United States, Europe, and Japan: In the United States there is 50 MHz of spectrum allocated to cellular radio within 800–900 MHz. Based on duopoly, each city has two licensed operators. Each one operates on a 25-MHz band. There are two bands, Band A and Band B. Each band consists of 416 channels. The channel bandwidth is 30 kHz. Among 416 channels, 21 channels are used for setting up and 395 are used for voice channels. • Analog: The frequency management of both Band A and Band B is shown in Table 75.5. • Digital: There are two potential systems, TDMA and CDMA shown in Table 75.1. In Europe the spectrum allocation is as shown in Table 75.2 and 75.3. In Japan the spectrum allocation is as shown in Table 75.4. TABLE 75.1 Specifications of TDMA and CDMA Systems TDMA CDMA Bandwidth per channel 30 kHz Bandwidth per channel 1.23 MHz Time slots 3 Speech coder 8 kbps(max.)—a variable rate vocoder Modulation p/4-DQPSK Forward radio channels Pilot (1) sync (1), paging (7), Speech coder 8 kbps—VSELP code traffic channels (55), total 64 (vector sum excited LPC*) channels Channel coding Rate 1/2 convolutional (13 kbps) Reverse radio channels Access (9), traffic channels (55) Total transmit rate 48 kbps per channel Power control Forward, reverse Equalizer Up to 40 ms Diversity Rake receiver * LPC = linear predictive code. TABLE 75.2 Specification of Three European Systems Analog England Scandinavia West Germany System TACS* NMT* C450 Transmission frequency (kHz) Base station 935–960 463–467.5 461.3–465.74 Mobile station 890–915 453–457.5 451.3–455.74 Spacing between transmission 45 10 10 and receiving frequencies (MHz) Spacing between channels (kHz) 25 25 20 Number of channels 1000 180 222 (control channel 21 ¥ 2); interleave used Coverage radius (km) 2–20 1.8–40 5–30 Audio signal Type of modulation FM FM FM Frequency deviation (kHz) ±9.5 ±5 ±4 Control signal Type of modulation FSK FSK FSK Frequency deviation (kHz) ±6.4 ±3.5 ±2.5 Data transmission rate (kbps) 8 1.2 5.28 Message protection Principle of majority Receiving steps are Message is sent again decision is employed predetermined when an error according to the is detected content of the message * TACS = total access cellular system; NMT = nordic mobile telephone