Programme’s After Market Services NHD–4 Series Transceivers Chapter 3 System Overview Original 11/97
NHD–4 System Overview PAMS Technical Documentation CONTENTS Page No Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cellular History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . AMPS Cellular Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Code Division Multiple Access (CDMA) . . . . . . . . . . . . . . . . . . . . . . . . . .
NHD–4 PAMS Technical Documentation System Overview List of Figures Page No Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. Figure 10. Figure 11. Figure 12. Figure 13. Figure 14. Figure 15. Figure 16. Figure 17. Figure 18. Figure 19. Figure 20. Figure 21. Figure 22. Figure 23. Figure 24. Figure 25. Figure 26. Figure 27. Figure 28. Figure 29. Figure 30. Figure 31. Figure 32. Figure 33. Figure 34. Figure 35. Figure 36. Figure 37. Figure 38.
PAMS NHD–4 System Overview Technical Documentation Acronyms ÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ
PAMS Technical Documentation NHD–4 System Overview Cellular History Mobile Radios have been in use for approximately 70 years and the cellular concept was conceived in the 1940s. Public cellular mobile radio was not introduced in the US until 1983. In the beginning of the twentieth century, mobile radios were limited to shipboard use due to the high power requirements and bulky tube radio technology. Automotive systems in the 1920s operated on 6 volt batteries with a limited storage capacity.
PAMS NHD–4 System Overview Technical Documentation AMPS Cellular Theory R. F. Communication BS Phone MTX Land Line Comms AMPS_1 Figure 1. AMPS: BS/MS/MTX The main objective of a cellular system is to provide communications to many mobile users. Communication between the Base Station and Mobile Phone is via a Radio Frequency (RF) link. A Mobile Telephone Exchange (MTX) is the interface between usually several base stations and Land line communications.
NHD–4 PAMS Technical Documentation System Overview High frequency signals will radiate electromagnetic waves from an antenna. Generally the higher the power the further the waves radiate. Our voice information is at a low frequency, these frequencies will not radiate. The solution is to put our information onto a high frequency carrier wave. Phone AMPS_3 Figure 3. AMPS: Voice/RF These signals can then be radiated out an antenna and carry our information to the receiver.
PAMS NHD–4 System Overview Technical Documentation Frequency Modulation AMPS_5 Unmodulated Carrier 1 kHz Mod Tone –8kHz +8 kHz Figure 5. FM Modulation The figure above represents the effect of a 1 kHz audio modulating tone on an RF carrier. The RF carrier in Figure 5 has a deviation of 8 kHz. A carrier deviation of 8 kHz means the frequency swings from plus 8 kHz to minus 8 kHz about the center frequency.
NHD–4 PAMS Technical Documentation System Overview Cellular Frequency Band AMPS_7 Phone TX RX 824.040MHz 869.040MHz 848.970MHz RX 893.970MHz TX Base Station Figure 7. AMPS: Cellular Frequencies The 800 MHz cellular band consists of two 25 MHz wide frequency blocks. The individual channel transmit and receive frequencies are spaced 45 MHz apart and each channel is 30 kHz wide. Note that the transmit frequencies for a Base Station are the receive frequencies for a cellular phone and vice–versa.
PAMS NHD–4 System Overview Technical Documentation Modulating Signals AMPS_9 Supervisory Audio Tone Type: Data Type: SAT Frequency: (FSK) 10 kbps Frequency: 5.97 kHz 6.0 kHz 6.
NHD–4 PAMS Technical Documentation System Overview Signaling tone (ST) Signaling tone is a plain 10 kHz tone. ST is used for signaling the base station when the mobile phone is “off hook”, conversation is ended “on hook”, hook flash, and handoff acknowledgment. When the mobile is being called,and is ringing, but has not been taken “off hook” a continuous ST is transmitted to the base station. When the mobile is taken “off hook”, answered, the ST is no longer sent.
NHD–4 System Overview PAMS Technical Documentation Line 1 in figure 11 is the state the mobile phone was at in figure 10. The mobile has found the strongest control channel and is “In service”. In line 2 the mobile phone transmits it’s ESN/MIN to the Base Station (only if not in its home area) using 10 kbytes/s data via the control channel. Line 3 shows the Base Station sending the mobile phone a data transmission confirming TX registration.
NHD–4 PAMS Technical Documentation System Overview CALL BS Channel 333 1. 2. Data A4D7 ”Service” Data ESN/MIN/Dialed # Data ESN/MIN/OK Goto 121/SAT=5970 Hz 3. Voice/SAT 4. 5. 1.8 sec (End Call) S.T. AMPS_12 Figure 12. AMPS: Call This is what happens when the mobile phone makes a “call”. As before the phone is “In service” on control channel 333 with Base Station A4D7. Line 2 shows the mobile phone sending a data stream to the Base Station that contains the mobile’s ESN/MIN/phone # dialed.
PAMS NHD–4 System Overview Technical Documentation Channel Reuse and SAT Frequencies Reused Voice Channels Different SAT freq prevents hook–up to other cell 313 1–50 333 101–150 B9CE A4D7 5970 Hz 320 201–250 315 151–200 327 51–100 BC43 Control Ch # Traffic Ch’s Base Station ID 8FB2 AMPS_13 319 101–150 796F B8C3 6030 Hz Figure 13. AMPS: Ch reuse & SAT Freq In this example Base Stations A4D7 and B8C3 are using the same traffic channels.
NHD–4 PAMS Technical Documentation System Overview 2nd IF Amp & FM Det 1st Mixer 881.52 MHz 869–894 MHz 45 MHz 455 kHz IF Amp LNA SAW Flter BW 25 MHz Xtal Filter Analog Modulation UHF VCO 914 – 939 MHz VHF VCO 180 MHz 2nd Clipper IF Amp Amp FM Det 90 2nd LO 44.545 MHz Ceramic Filter 455 kHz o Ringing Ckt RX 180 mhZ Duplexer 914–939 mhZ TX SAW Filter Power Amplifier & Driver SAW Filter TX gain control Driver Amps 2 90 MHz TX Mix 824–840 MHz 824–840 MHz CDAGCT AMPS_15.
NHD–4 System Overview PAMS Technical Documentation An Audio Analyzer is used to determine the phones SINAD response. Minimum receiver sensitivity is defined as the RF level (–116 dBm) that, when modulated in a specified manner (8 kHz deviation with a 1 kHz tone) will result in a SINAD of at least 12 dB. SINAD is an acronym for Signal, Noise and Distortion, not just the signal to noise ratio.
NHD–4 PAMS Technical Documentation System Overview Code Division Multiple Access (CDMA) Amplitude Time Channelization – FDMA RX Ch1 Amplitude RX Ch...n TX Ch...n Frequency Channelization – TDMA Time 3 1 2 RX Ch1 TX Ch 1 3 1 2 3 1 2 RX Ch...n TX Ch 1 3 1 2 TX Ch...n Frequency Channelization – CDMA Time Forward Link B.S. M.S. Amplitude PN Sequence (short code) PN Offset 1 PN Offset 2 ... PN Offset 512 Channelization – CDMA Reverse LinkM.S. Amplitude B.S.
PAMS NHD–4 System Overview Technical Documentation The frequency reuse factor is a number representing how often the same frequency can be reused. To provide acceptable call quality, a Carrier–to–Interference ratio (C/I) of at least 18 dB is needed. Practical results show that in most cases to maintain a 18 dB (C/I) a frequency reuse factor of 7 is required (see figure 18).
NHD–4 PAMS Technical Documentation System Overview The AMPS, DAMPS, and GSM capacity examples in figure 17 assume that only one channel out of every seven can be used. In a crowded metropolitan area, cellular base stations are arranged like the top part of figure 18. Each base station is surrounded by seven others so only one out every 7 channels can be used or adjacent channel interference will occur.
PAMS NHD–4 System Overview Technical Documentation Quadrature Phase Shift Keying – QPSK Forward link transmissions from the Base Station (BS) to the Mobile Subscriber (MS) use QPSK modulation. QPSK is the sum of Two Binary Shift Keyed (BPSK) signals. Figure 19 shows how a BPSK signal is made up.
NHD–4 PAMS Technical Documentation System Overview I DATA SIN CARRIER INPUT Values of Data Channels are –1 and 1, not 0 and 1 o 90 Hybrid COS Σ CDMA04.DRW Q DATA For the reverse link the Q data is delayed by 1/2 clock chip. This modulation is called OQPSK (Offset Quadra Phase Shift Keying) Figure 20. I/Q Modulator In Figure 20 the 90 phase shifter is used to generate the sine and cosine channel reference frequency.
PAMS NHD–4 System Overview Technical Documentation The CDMA Signal CDMA Transmitter 10 kHz BW 1.25 MHz BW Baseband Data Encoding & Interleaving 9.6 kbps 19.2 kbps ÏÏÏÏÏÏ ÏÏÏÏÏÏ Background Noise CDMA Receiver 1.25 MHz BW 10 kHz BW ÑÑÑÑ ÌÌÌÌ ÏÏÏÏ ÌÌÌÌÌ ÌÌÌÌ ÑÑÑÑ ÑÑÑÑÑ ÏÏÏÏÏ ÏÏÏÏ ÌÌÌÌÌ Walsh Code Spreading 1228.8 kbps External Interference Walsh Code Correlator 1228.
NHD–4 PAMS Technical Documentation System Overview When the wanted CDMA signal, “yours”, is received the correlation receiver recovers “your” signal and rejects the rest. Looking at figure 21, the upper right most part of the drawing shows what happens to the unwanted signals. The unwanted signals are not de–spread so that each interfering signal only contributes a little to the noise floor while “your” wanted signal is de–spread and will have an acceptable signal–to–noise ratio.
PAMS NHD–4 System Overview Technical Documentation The CDMA Forward Link 20 MSEC CDMA Forward Link BLOCKS Convolutional Interleaver XOR Encoder 1/2 Rate 9.6 19.2 19.2 kbps kbps kbps Vocoded Speech data Long Code Generator 1.2288 Mbps Long Code Decimator 1 of 64 bits 1.2288 Mbps I Short Code Walsh Cover XOR Power Control Bit I Channel Lo Pass Filter MUX 800 Hz 1 in 24 Decimator To I/Q Modulator 1.2288 Mbps Lo Pass Filter Q Channel Walsh Code Generator Q Short Code 1.
NHD–4 PAMS Technical Documentation System Overview Vocoder CDMA takes advantage of quiet times during speech to raise capacity. A variable rate VOCODER is used; the vocoder’s output is at 9600 BPS when the user is speaking. When the user pauses, or is listening, the data rate drops to 1200 BPS. The data rates of 2400 and 4800 BPS are also used but not as often as the other two. The data rate is based on speech activity and complexity. A decision is made on the data rate every 20 msec.
PAMS NHD–4 System Overview Technical Documentation Interleaver Data In 1 2 3 Data Out 4 5 5 Interleaver 4 1 3 CDMA08.DRW 2 Figure 24. Interleaver Interleaving is the process of shuffling the data before transmission with a corresponding un–shuffle on the receiving end. The purpose is to spread the bit errors. Bit errors tend to come in bursts due to fading, rather than uniformly spread in time.
NHD–4 PAMS Technical Documentation System Overview The forward link Short Code is the same for all base stations. However a specific mask is AND’ed with the output of the code generator to create a unique short code. Even though the specific mask does not change the PN pattern the code is considered unique relative to system time. This means that each specific mask will shift the PN code to a unique delay with respect to system time and in this way the shifted PN code is considered unique.
PAMS NHD–4 System Overview Technical Documentation ÁÁÁÁ ÁÁ ÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁ ÁÁÁ ÁÁÁÁÁÁÁ ÁÁÁÁ ÁÁ ÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁ ÁÁÁ ÁÁÁÁÁÁÁ ÁÁÁÁ ÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁ ÁÁÁ ÁÁÁÁÁÁÁ ÁÁ ÁÁÁÁ ÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁ ÁÁÁ ÁÁÁÁÁÁÁ ÁÁ ÁÁÁÁ ÁÁ ÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁ ÁÁÁ ÁÁÁÁÁÁÁ ÁÁÁÁ ÁÁ ÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁ ÁÁÁ ÁÁÁÁÁÁÁ ÁÁÁÁÁÁ ÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁ ÁÁÁ ÁÁÁÁÁÁÁ ÁÁÁÁ ÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁ ÁÁÁ ÁÁÁÁÁÁÁ ÁÁ ÁÁÁÁ ÁÁ ÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁ ÁÁÁ ÁÁÁÁÁÁÁ ÁÁÁÁ ÁÁ ÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁ ÁÁÁ ÁÁÁÁÁÁÁ ÁÁÁÁ ÁÁ ÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁ ÁÁÁ ÁÁÁÁÁ
NHD–4 PAMS Technical Documentation System Overview The Interleaver changes the data order so only bits instead of whole words would be lost because of data errors. The Long Code Generator generates a code that is 242 bits long. This code runs at 1.2288 Mbps and takes about 41.5 days before it repeats. The PN (Pseudo–random) code is decimated by a factor of 64 that means only one out of 64 bits is XOR’ed with the output of the Interleaver. The data rate at this point is still 19.2 ksps because two 19.
NHD–4 System Overview PAMS Technical Documentation Walsh codes have the desirable characteristic of being “orthogonal” to each other. What the heck does that mean(this is a rhetorical question)? ORTHOGONAL Walsh Codes: when simultaneously transmitted they produce minimal interference to other users. Look at the rows across in code set 4, any two rows have an equal number of matches and mismatches. When correlation occurs between codes (they match up) they will yield a cross correlation coefficient of 1.
NHD–4 PAMS Technical Documentation System Overview Orthogonal Functions Two values are orthogonal if the result of exclusive–ORing them results in an equal number of 1’s and 0’s. Figure 30 uses the number 2 code, 0 1 0 1, in the Walsh code set 4 to “Orthogonally Spread” some user input data. Each bit of user input data is exclusive–OR’ed with the number 2 Walsh code that will result in TX Data shown in Figure 30.
PAMS NHD–4 System Overview Technical Documentation User A Walsh Encoding Example User B User B data 0110 User A data 1011 +1 For a 1 input, use Code 00 +1 0 0 0 –1 W +1 1 For a 1 input use code 01 1 = 2 0 0 – User A 0 1 – User B –1 For a 0 input use code 10 1 1 For a 0 input, use Code 11 0 –1 +1 Channel A Voice data Channel A Walsh Encoded Voice Data 1 1 0 Channel B Voice Data 1 0 1 0 0 0 0 0 0 Channel B Walsh encoded Voice data 1 1 0 0 +1 1 0 +1 1 1 0 0 1 0
NHD–4 PAMS Technical Documentation System Overview Here is how the “bipolar” addition works: Voice data 1 0 1 1 bipolar Walsh code –1–1 +1+1 –1–1 –1–1 Walsh encoded data 0 0 1 1 0 0 0 0 The voice data is added to both bipolar Walsh code numbers. The example is for User A. If the two Walsh encoded voice data channels are added together the result is a data stream that varies between +2 and –2.
PAMS NHD–4 System Overview Technical Documentation To calculate User B’s first data bit multiply (0 X –1) and (–2 X 1) which equals zero, minus two waveform. Find the area under the curve, (0 + (–2)) / 2 = –1, which is User B’s first data bit. It has been stated that Walsh codes are orthogonal and that this property results in zero cross talk between Walsh code signals. Using bipolar numbers multiply Walsh code “00” with Walsh code “01”.
NHD–4 PAMS Technical Documentation System Overview ÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ Á
PAMS NHD–4 System Overview Technical Documentation ÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ Á
NHD–4 PAMS Technical Documentation System Overview ÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ Á
NHD–4 System Overview PAMS Technical Documentation The “Pilot Channel” can be compared with the control channels used in analog. The “Pilot Channel” is unmodulated Walsh code zero spread with Short Code that has a unique mask applied in order for mobiles to identify cells from each other. Pilot channel power is the strongest channel from the base station, with about 20% of the total output power.
NHD–4 PAMS Technical Documentation System Overview W0 Pilot Channel: All 0’s + 1.2288 MHz I Channel Short Code Pilot PN Sequence W32 Convolutional Encoder Sync Channel Data 1200 bps 1.2288 MHz 4800 bps Interleaver + + W1–7 Paging Channel Data 9.6 kbps Convolutional 4.8 kbps Encoder 2.4 kbps Paging Channel Long Code Mask Forward Traffic Channel Data 9.6 kbps 4.8 kbps 2.4 kbps 1.2 kbps Convolutional Encoder 1.2288 MHz 19.
PAMS NHD–4 System Overview Technical Documentation CDMA Reverse Link 20 msec blocks I Short Code Convolutional Encoder Interleaver 6–bit words @ 4.8 k/s Vocoded 9.6 1/3 kbps rate 28.8 28.8 kbps kbps Speech Data Walsh Code 63 Walsh Code 62 Walsh Code 61 Data Burst Walsh Code 2 307.2 Randomizer Walsh Code 1 kbps Walsh Code 0 x 1/2 Chip Delay 1.2288 Mbps x I x 1/2 Q Short Code 1.2288 Mbps Long Code Figure 35.
PAMS Technical Documentation NHD–4 System Overview Reverse Link Error Protection To improve the reverse link performance a one–third rate convolutional encoder is used. This encoder has one 9600 bps input and three 9600 bps outputs which when combined result in a 28.8 kbps data stream. Each data bit is encoded with 3 error correction bits to improve the error correction rate. The forward link uses one–half rate encoding.
PAMS NHD–4 System Overview Technical Documentation Mobile Phone Operation When a CDMA mobile scans for the strongest Pilot Channel signal, the scanning is done in time rather than frequency scanning like an analog phone does. Once the strongest Pilot channel has been located, Sync Channel information is demodulated. The sync channel contains information the mobile needs in order to decode the Paging Channel.
PAMS Technical Documentation NHD–4 System Overview Master (System) start time is shown on both circles but the mobile does not know System start time until it decodes the Sync channel. Remember that both the Pilot and Sync channels do not contain a Long Code so they both repeat at the same rate of 26.67 msec. The mobile starts decoding the Synch channel information of the strongest cell site when it acquires that cell’s Pilot channel.
NHD–4 System Overview PAMS Technical Documentation CDMA Channel List Message: The CDMA channel list reports the number of CDMA frequencies supported by the cell station in use as well as surrounding cell site frequencies and configurations. Slotted Page Message: The Slotted and Non–slotted page messages allow the cell site to page CDMA phones for incoming calls. CDMA mobiles operating in the slotted mode must first register with the cell site before they can be paged.
PAMS Technical Documentation NHD–4 System Overview The second base station is a mini–cell and therefore transmits at a lower power. The mobile would transmit a higher power than necessary to the mini–cell because the weaker signal would be interrupted as a distant station. This problem is taken care of after the mobile has located the strongest base station. Information contained in the Sync Channel of each cell site transmits its characteristics for power control.
PAMS NHD–4 System Overview Each frame is divided into 16 Power Control Groups Technical Documentation Full Rate 9.6 kbps CDMA Frame = 20 ms 16 Power Control groups Half Rate 4.8kbps 8 Power Control Groups Each Power Control Group contains 1536 chips (represents 12 encoded voice data bits Quarter Rate 2.4kbps 4 Power Control Groups Eighth Rate 1.2kbps 2 Power Control Groups Average power is lowered 3 dB for each lower data rate Figure 37.
NHD–4 PAMS Technical Documentation System Overview One more advantage of CDMA mobiles is utilized when a hand–off to another base station is necessary, a make–before–break soft hand–off is used. The rake receiver constantly searches for and measures multi–path and neighboring signals. The multi–path signals are time adjusted then combined for a stronger total signal. The neighboring cell site signals are used to determine the best choice when a handoff when necessary.
NHD–4 System Overview PAMS Technical Documentation The pilot strength message starts a soft hand–off. When the pilot strength message is received; base station A passes this request to the MTSO (Mobile Telephone Switching Office). The MTSO passes the request to station B to see if a traffic channel is available for the soft hand–off request. CDMA Soft Hand–off If a channel is available, cell site B sends the Walsh Code that will be assigned for the soft hand–off to the MTSO.
