Nokia 2170 Service Manual overview
Programme’s After Market Services
NHP–4 Series Transceivers
Chapter 3
System Overview
Issue 1 04/99
NHP–4
System Overview
Technical Documentation
CONTENTS
Acronyms 3–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cellular History 3–5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Code Division Multiple Access (CDMA) 3–6. . . . . . . . . . . . . . . . . . . . . . . . . .
Quadrature Phase Shift Keying – QPSK 3–9. . . . . . . . . . . . . . . . . . . . . . .
The CDMA Signal 3–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Processing Gain 3–11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The CDMA Forward Link 3–12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
V ocoder 3–13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Convolutional Encoder 3–13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Interleaver 3–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PAMS
Page No
PN Code Generation 3–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Long Code Scrambling 3–16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Walsh Code User Channelization 3–16. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Walsh Codes 3–17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Orthogonal Functions 3–18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Short Code Spreading 3–24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Forward Link Channel Format 3–24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CDMA Reverse Link 3–27. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Data Burst Randomizer 3–27. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reverse Link Error Protection 3–28. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
64–ary Modulation 3–28. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reverse Channel Long Code Spreading 3–28. . . . . . . . . . . . . . . . . . . . . . .
Reverse Channel Short Code Spreading 3–28. . . . . . . . . . . . . . . . . . . . . .
Mobile Phone Operation 3–29. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pilot Channel 3–29. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sync Channel 3–30. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Paging Channel 3–30. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Page 3–2
CDMA Call Initiation 3–31. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reverse Link Open Loop Power Control 3–31. . . . . . . . . . . . . . . . . . . . . . .
CDMA Call 3–32. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reverse Link Closed Loop Power Control 3–32. . . . . . . . . . . . . . . . . . . . .
CDMA Variable Rate Speech Coder 3–32. . . . . . . . . . . . . . . . . . . . . . . . . .
Mobile Power Bursting 3–32. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The Rake Receiver 3–33. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CDMA Hand–offs 3–34. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Issue 1 04/99
PAMS
NHP–4
Technical Documentation
System Overview
List of Figures
Figure 1. TDMA & CDMA Freq and time domain 3–6. . . . . . . . . . . . . . . . . . . .
Figure 2. CDMA Capacity gains 3–7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 3. TDMA & CDMA Structure 3–8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 4. BPSK Modulator 3–9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 5. I/Q Modulator 3–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 6. CDMA Waveforms 3–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 7. CDMA Forward Link 3–12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 8. Convolutional encoder 3–13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 9. Interleaver 3–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 10. PN Code generator 3–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 11. PN Code generator w/mask ckt. 3–15. . . . . . . . . . . . . . . . . . . . . . . . .
Page No
Figure 12. Mask offset example 3–16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 13. CDMA Forward Link 3–16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 14. Walsh code example 3–17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 15. Orthogonal Functions. 3–18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 16. Walsh Encoding Example 3–19. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 17. Walsh Decoding Example 3–20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 18. Definition of orthonogonality 3–21. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 19. Forward Link Channel Format 3–26. . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 20. CDMA Reverse Link 3–27. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 21. CDMA Pilot & Synch Channel Timing 3–29. . . . . . . . . . . . . . . . . . . .
Figure 22. Mobile Power Bursting 3–33. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 23. CDMA Hand–off 3–34. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Issue 1 04/99
Page 3–3
NHP–4
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
System Overview
Acronyms
PAMS
Technical Documentation
AMPS
BS
ББББББББ
CDMA
CTIA
DAMPS
ББББББББ
DTMF
FDMA
GSM
ББББББББ
HLR
ISDN
MS
ББББББББ
MSC
MTSO
MTX
ББББББББ
NADC
Advanced Mobile Phone System
Base Station
БББББББББББББББББББББ
Code Division Multiple Access
Cellular Telecommunications Industry Association
Digital Advanced Mobile Phone System
БББББББББББББББББББББ
Dual Tone Multi Frequency
Frequency Division Multiple Access
Global System for Mobile communications
БББББББББББББББББББББ
Home Location Register
Integrated Services Digital Network
Mobile Station (Cellular phone)
БББББББББББББББББББББ
Mobile Switching Center (see MTX also)
Mobile Telephone Switching Office
Mobile Telephone Exchange (see MSC also)
БББББББББББББББББББББ
North American Digital Communications (IS–54 DAMPS)
PCH
PN Code
ББББББББ
PSTN
RF
SAT
ББББББББ
ST
TCH
TS
ББББББББ
VLR
VOCODER
VOCODER
Paging Channel
Pseudo random Noise Code
БББББББББББББББББББББ
Public Switched Telephone Network
Radio Frequency
Supervisory Audio Tone (5970, 6000 and 6030 Hz)
БББББББББББББББББББББ
Signaling Tone (10 kHz)
Traffic CHannel
Time Slot
БББББББББББББББББББББ
Visitor Location Register
VOice COder DEcodeR
VOice CODER
Page 3–4
Issue 1 04/99
PAMS
NHP–4
Technical Documentation
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.
One of the first useful means of automotive mobile radio occurred in 1928 by the
Detroit police department. Transmission was broadcast from a central location and
could only be received by the mobile police radios.
Introduction of the first two way mobile application was delayed until 1933. This
simplex AM (Amplitude Modulation) push to talk system was introduced by the
police department in Bayonne, New Jersey. The first FM (Frequency Modulation)
mobile transmission (two frequency simplex) was used by the Connecticut State
Police at Hartford in 1940.
The first step towards mobile radio connection with the land line telephone network
was established in St. Louis in 1946. It was called an “urban” system and only
supported three channels.
In 1976, New York City had only 12 radio channels that supported 545 subscribers
with a waiting list of 3700.
In the 1970s, available cellular spectrum was constrained to frequencies above 800
MHz due to equipment design limitations and poor radio propagation characteristics
at frequencies above 1–GHz, this resulted in the allocation of the 825–890 MHz
region.
In 1974, 40 MHz of spectrum was allocated for cellular service and in 1986, an
additional 10 MHz of spectrum was added to facilitate expansion. The present
frequency assignments for the US Cellular system mobile phone is
824.040–848.970 MHz transmit and 869.040–893.970 MHz receive These bands
have been frequency divided (FDMA) into 30 kHz channels. This results in a
maximum capacity of 832 channels. These channels were then divided into two
groups with 416 channels assigned to each system.
Issue 1 04/99
Page 3–5
NHP–4
System Overview
Code Division Multiple Access (CDMA)
PAMS
Technical Documentation
Amplitude
RX Ch1 RX Ch...n TX Ch 1 TX Ch...n
Amplitude Time
Amplitude
Time
Time
Channelization – FDMA
Channelization – TDMA
3
2
1
3
2
1
3
2
1
TX Ch...nTX Ch 1RX Ch...nRX Ch1
Channelization – CDMA
Forward Link B.S. M.S.
PN Offset 1 PN Offset 2 PN Offset 512
. . .
Frequency
3
2
1
Frequency
PN Sequence
(short code)
Channelization – CDMA
Amplitude
Time
CDMA01.DRW
Reverse LinkM.S. B.S.
Allows Channalization
and privacy
42
2
possible
PN Sequence
(long code)
Figure 1. TDMA & CDMA Freq and time domain
With FDMA Channelization (Analog AMPS), a channel is 30 kHz wide, this where all
the signal’s transmission power is concentrated. Different users are assigned
different frequency channels. FDMA is the acronym for Frequency Division Multiple
Access. Interference to and from adjacent channels is limited by the use of
bandpass filters that only pass signal’s within a specified narrow frequency band
while rejecting signals at other frequencies. The analog FM cellular system AMPS,
uses FDMA.
The US 800 MHz cellular system divides the allocated spectrum into 30 kHz
bandwidth channels. Narrowband FM modulation is used with AMPS, resulting in 1
call per 30 kHz of spectrum. Because of interference, the same frequency cannot
be used in every cell.
Page 3–6
Issue 1 04/99
PAMS
NHP–4
Technical Documentation
System Overview
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. Please note that C/I
is carrier to interference, not signal to noise ratio The resulting capacity is one call
per 210 kHz of spectrum in each cell.
With TDMA, a channel consists of a time slot in a periodic train of time intervals
making up a frame. A given signal’s energy is confined to one of these time slots.
The IS–54B TDMA standard provides a basic modulation efficiency of three voice
calls per 30 kHz of bandwidth. The resulting capacity is one call per 70 kHz of
spectrum or three times that of the analog FM system.
With CDMA each signal consists of a different pseudo random binary sequence that
modulates the carrier, spreading the spectrum of the waveform. A large number of
CDMA signals share the same frequency spectrum. The signals are separated in
the receivers by using a correlator that accepts only signal energy from the selected
binary sequence and de–spreads its spectrum simultaneously. The other users’
signals, whose codes do not match, are not de–spread and as a result, contribute
only minimally to the noise and represent a self–interference generated by the
system. The forward link (B.S. to M.S.) “channels” are separated by offsets in the
short code PN sequence. Reverse link channels are separated by different long
code PN sequences. A detailed description of the forward and reverse links is
given later.
CDMA = 1.5 MHz 1 CDMA channel + 1.2288MHz
Capacity varies between 30 to 40 calls per CDMA
channel. Actual capacity depends Rho, processing
gain, error correction coding gain of M.S. vs signals
in cell and external cell signals.
AMPS = 1.5 MHz / 30kHz = 50 Channels
Capacity = 50 Channels / 7 (1 in 7 Frequency Reuse)
AMPS = 7 calls
DAMPS = 1.5 MHz / 30 kHz = 50 Channels
Capacity = 50 Channels / 7 x 3 Time Slots
DAMPS = 21 calls
GSM = 1.5 MHz / 200 kHz = 7 Channels
Capacity = 7 Channels / 7 x 8 Time Slots
GSM = 8 calls
Figure 2. CDMA Capacity gains
CDMA Capacity
Why should NOKIA go to so much trouble to develop CDMA? CAPACITY! To see
how CDMA increases capacity over present 800 MHz systems (AMPS and DAMPS)
lets look at a 1.5 MHz span of frequencies and compare. A CDMA frequency
channel is 1.2288 MHz wide however to provide guard bands in order to reduce
potential interference with adjacent analog channels a total of 1.5 MHz will be used.
Issue 1 04/99
Page 3–7
NHP–4
System Overview
Technical Documentation
PAMS
The AMPS, DAMPS, and GSM capacity examples 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 3 Each base station is surrounded
by seven others so only one out every 7 channels can be used or adjacent channel
interference will occur. However, such is not the case for CDMA because all users
on a “CDMA Channel” operate on the same frequency. I’ve just used the word
“Channel” in a different way. Users in a given CDMA channel are separated by
different PN code sequences. According to information at the present time there
four designated CDMA frequency channels, so users on a given frequency channel
operate on the same frequency and are separated by different PN code sequences
which are also called “Channels”.
2
2
7
1
6
5
7
3
6
4
2
7
1
6
5
3
1
4
5
7
3
6
4
CDMA Cell Structure
Transmission range of
any given celll
1
1
ANALOG & TDMA Cell Structure
Transmission range of
any given cell
2
3
1
4
5
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
CDMA03.DRW
Page 3–8
Figure 3. TDMA & CDMA Structure
Issue 1 04/99
PAMS
NHP–4
Technical Documentation
System Overview
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 4 shows how a BPSK signal is made up.
180
Time
0
TT
TT
Reference
carrier
input
Carrier
input
Carrier
input
DAMPS_4
A
T1 T2
B
++ ++
0 deg
–– ––
C
++
0 deg
––
Binary Phase Shift Keying
D1
D3
D4
D2
Binary input
D1 (on)
D3 and D4
(off)
D2 (on)
Binary 1
D1 (off)
D2 (off)
Binary 0
––
D3/D4
(on)
++
Modulator
output
Carrier
output
180 deg
Carrier
output
Binary
input
BPSK
output
Degrees
Radians
0 deg
10 1 10
0
TT
180
0
TT
TT
Binary input Output phase
Logic 0 180 deg
Logic 1 0 deg
Figure 4. BPSK Modulator
Before starting any explanation about phase modulation a convention needs to be
established that will carry on throughout this study guide. Digital signals are
generally generated by use of a modulator that generates a sine and a cosine
channel and scales each channel by a factor that ranges from –1 to +1. What
the last sentence means is that the values of Data Channels are –1 and +1, not
0 and 1. A logic one will be “plus one” and a logic zero will be “minus one”.
In drawing ”B” diodes D1 and D2 are forward biased into conduction with a logic
one. Transformer’s T1 and T2 are connected together in an in–phase condition. In
this case the output carrier’s signal would have the same phase as the input.
In drawing “C”diodes D3 and D4 are forwarded biased into conduction with a logic
zero. The output of T1 is cross connected to the input of T2 which will result in the
output being 180 degrees out of phase with the input signal.
Issue 1 04/99
Page 3–9
NHP–4
System Overview
PAMS
Technical Documentation
I DATA
SIN
CARRIER
INPUT
Values of Data Channels
are –1 and 1, not 0 and 1
90
Hybrid
COS
o
Σ
For the reverse link
the Q data is delayed
CDMA04.DRW
Q DATA
by 1/2 clock chip. This
modulation is called
OQPSK (Offset Quadra
Phase Shift Keying)
Figure 5. I/Q Modulator
In Figure 5 the 90 phase shifter is used to generate the sine and cosine channel
reference frequency. The two signal paths are called the “In phase” and the
“Quadrature phase” paths, therefore the name, I/Q modulator.
The CDMA Signal
CDMA
Transmitter
CDMA
Receiver
1.25 MHz BW1.25 MHz BW
10 kHz BW10 kHz BW
Baseband
Data
9.6 kbps 19.2 kbps 1228.8 kbps
Background Noise
Encoding &
Interleaving
Walsh Code
Spreading
External Interference Other cell interference Other User Noise
Interference Sources
Walsh Code
Correlator
1228.8 kbps
Decode & De–
interleaving
19.2 kbps 9.6 kbps
Baseband
Data
CDMA05.DRW
Figure 6. CDMA Waveforms
To explain CDMA, some terms will have to be used that most persons are not
familiar with, but have patience they will be given a full explanation later in this Study
Guide. Forward link (BS to MS) CDMA starts with a narrowband signal that is
digitized speech. In this example the
full rate speech data rate
of 9600 bps is
shown.
Page 3–10
Issue 1 04/99
PAMS
NHP–4
Technical Documentation
Speech data rates from the VOCODER can vary from 1200 BPS to 9600 BPS when
using “Rate Set One” and 14.4, 7.2, 3.6, and 1.8 kbps when using “Rate Set Two”.
A specialized digital code called a Walsh Code provides “user” channelization for the
forward link (B.S to M.S.) and is used to encode the reverse link (B.S. to M.S.) user
data. The short code PN sequence
reverse links. The short code also provides channelization for BASE STATIONS on
the forward link by using a masking circuit. Masking will be explained later.
Processing Gain
One of the unique aspects of IS–95 standard CDMA is 21 dB of processing gain.
Processing gain is computed by using the formula 10 log(spread data rate) divided
by (Symbol rate). [10 log (1,228,800 / 19.2kBPS) = 21 dB]. If you calculate the
processing gain using the numbers in the last sentence the answer is 18 dB. The
extra 3 dB is comes from the same data being transmitted by the Q channel. If rate
set 2 is used the processing gain is 19.31 dB. When “your” CDMA signal is
transmitted all other CDMA signals along with background noise and any spurious
signals are considered interference.
SPREADS
the baseband for both forward and
System Overview
When the wanted CDMA signal, “yours”, is received the correlation receiver
recovers “your” signal and rejects the rest. Looking at Figure 6, 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. This is where the processing gain comes into
play. The processing gain is 21 dB and it takes a signal–to–noise ratio of about 7
dB for acceptable voice quality. This leaves 14 dB of processing gain to extract
“your” signal from the noise.
Here are some of the differences between CDMA and analog FM (AMPS).
Multiple users are on one frequency at the same time. RF engineers have spent a
lot of time and effort trying to keep signals on one channel so that adjacent channel
signals would not cause interference. CDMA technology places a great many
conversations (signals) on the same frequency.
In CDMA a channel is defined by various digital codes in addition to having different
frequencies. Analog FM channels are defined by different frequencies only.
An analog FM (AMPS) cell site has a hard limit on the number of users it can
accommodate, only one call per frequency channel. CDMA has a soft capacity
limit. If cells surrounding a heavily loaded cell are lightly loaded then the heavily
loaded cell site can accommodate additional users. CDMA has a soft limit because
less “other cell” interference causes the total interference to be less. More calls can
also be accommodated at the expense of lower voice quality (S/N), this because
each additional user adds only a small amount of interference to the total.
Issue 1 04/99
Page 3–11
Loading...