3- microwave and radio

Optical Network Broadband-Ethernet PricipleMicrowave Part [ AM ; protection, SNCP , LMSP ]
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
AM Function
The AM function adjusts the modulation scheme according to the quality of the channel , In the case of the same channel spacing,
the microwave service bandwidth varies with the modulation mode. The higher the modulation efficiency, the higher the bandwidth
of the transmitted services is. In this manner, the anti-interference capability of the radio link is improved and the link
availability of the services with a higher priority is ensured.
The AM technology adopted by the OptiX RTN 950 has the following features:
> The AM technology can use the QPSK, 16QAM, 32QAM, 64QAM, 128QAM, and 256QAM modulation mode.
> The lowest modulation mode (also called "reference mode") and the highest modulation mode (also called "nominal mode") actually used by the AM can be configured.
> When the modulation modes of AM are switched, the transmit frequency, receive frequency, and channel spacing do not change.
> When the modulation modes of AM are switched, the step-by-step switching mode must be adopted.
> When the AM switches the modulation modes to a lower one, the services with the low priority are discarded but no bit errors or slips occur in the services with the high priority. The speed of switching the modulation modes meets the requirement for no bit error in the
case of 100 dB/s fast fading.
Purpose\ to use the microwave frequency resources more efficiently and to provide
a higher valid bandwidth, according to the propagation condition of air interface,
the modulation mode is automatically changed to ensure that the services are transmitted
to the greatest extent.
> When the AM function is enabled, the Hybrid microwave supports the 1+1 protection and N+1 protection and XPIC function.
> When the XPIC function is enabled, the XPIC workgroup can be configured only on the channel spacing of 28 MHz or 56 MHz.
Capacity
Time
99.999%
Voice
AM Working Principle (Before the Switching)
1. The service is scheduled to the IF interface of the IF board and then multiplexed into the microwave frame at the MUX unit.
2. The microwave frame is transmitted to the opposite end over the Tx path after being modulated by the IF unit.
3. The Rx path of the opposite end receives the IF signal and then checks the quality of the received signal based on the received signal to noise ratio (SNR). In the case of the current modulation scheme, the quality of the received signal is considered to be degraded if the value of the received SNR is lower than the preset threshold. In this case, the opposite end
sends a signal that indicates the quality of the received signal to the AM engine.
4. The AM engine at the opposite end sends the microwave frame to the local end after the switching indication signal is inserted into the overhead of this microwave frame.
5. The IF unit at the local end processes the received IF signal and sends the AM switching indication signal to AM engine at the local end.
6. The AM engine sends the switching indication signal to the MUX unit to enable the MUX unit and the air interface to change the modulation scheme, as shown
System gain is decreased while modulation increased and service bandwidth also ,
under bad weather condition or even an interference the Modulation mode is down shifted
to conserve the highest priority service and drop low priority services giving granularity of different
services types as in below diagram
voice 99.999%
video 99.995 %
data 99.99 %
in the AM technology , modulation mode switched step by step according to signal to noise ration
( SNR ) at the receiver , to ensure smooth jitter and bit error free events in the switching , the system
does not switch the modulation mode immediately in all cases that SNR reaches the relevant
threshold , instead , certain AM margin is added , so final SNR is called SNR threshold ,
to prevent frequent modulation switching , SNR value of the downshift is lower than SNR value
of the up shift , another powerful feature that the site participate in the formation of the AM link ,
start to search for optimum modulation mode it can use in the transmission direction , while it can
use another low modulation type in the receiving direction in case the opposite site do not got
AM function enabled, so that at an instance Huawei MW site can have two types of carrier
one used for modulation and other used for demodulation.
On the NMS, modulation mode can be set to lowest modulation mode (Guaranteed mode)
, and the highest modulation mode ( Full-Capacity mode) , for convenient description ,
the modulation mode for meeting the highest link availability of the service capacity of the
customer is called the reference mode , By default reference mode is considered as the
Guaranteed mode.
Up shift switch threshold from QPSK-> 16-QAM
Up shift switch threshold from 16-QAM> 32-QAM
Working in 16-QAM
Working in 32-QAM
Working in 64-QAM
UP-Shift
Down-Shift
QPSK
16-QAM
32-QAM
64-QAM
128-QAM
256-QAM
QPSK Area
16-QAM Area
32-QAM Area
64-QAM Area
128-QAM Area
256-QAM Area
System switched to use 16-QAM while it can support up to 32-QAM used as margin
Probability of working duration in each mode is almost the same.
QPSK
16-QAM
32-QAM
64-QAM
128-QAM
256-QAM
Formula of Calculating Required SNR at the receiver
S/N = THR + k*B - F
THR = Receiver threshold , k = Boltzmann Constant , B = Signal Bandwidth ,
F = Noise Factor
After the AM Function is Enabled , S/N’ = ( THR + AM ) + k*B – F , thus the New
S/N’ required in the Design for each up-shift or down-shift switching has an added
Margin = AM , saving switching criteria has hitless switching.
where
(no interference) [dBW]
B - the IF bandwidth in Hertz
F - the receiver noise figure in decibel
Receiver Sensitivity – IFU2
Receiver Sensitivity IF1
Receiver Sensitivity IFX2
Receiver Sensitivity IFX2
Noise factor of the receiver
RSL@-65dBm
HP(dB)
XMC-2(dB)
SP(dB)
SPA(dB)
LP(dB)
XMC-1(dB)
6GHz
NA
NA
NA
7.0
NA
NA
7GHz
7.0
NA
7.5
7.0
7.0
NA
8GHz
7.0
NA
7.0
7.0
NA
11GHz
6.5
NA
7.0
7.0
7.0
NA
13GHz
6.5
NA
7.0
7.0
7.0
NA
15GHz
6.5
6.5
7.0
7.0
7.0
6.5
18GHz
6.5
NA
7.0
7.0
7.0
NA
23GHz
7.0
7.1
7.5
7.5
7.5
7.1
26GHz
7.0
NA
7.5
NA
NA
NA
32GHz
8.0
NA
NA
NA
NA
NA
38GHz
9.0
NA
10.0
NA
NA
NA
FKTB
dBm
= -174 + 10logB+NF. B indicates the bandwidth at the symbol rate, and NF indicates the preceding noise factor.
CS
7M
14M
HP
XMC-2
SP
SPA
LP
XMC-1
HP
XMC-2
SP
SPA
LP
XMC-1
6GHz
FKTB
28M
56M
HP
XMC-2
SP
SPA
LP
XMC-1
HP
XMC-2
SP
SPA
LP
XMC-1
6GHz
AM Sensitivity data
AM Sensitivity data
AM Sensitivity data
the presence of interfering signals increases the
receiver's threshold level for a given bit-error ratio (BER).
When an interfering signal is present, the S/I ratio is decreased, giving a receiver threshold degradation. To maintain the system performance (for an unchanged
fading margin) the receiver input level during fading free time must be increased. Maintaining the receiver input unchanged would degrade the BER performance.
Decreasing modulation scheme guarantee the
Increase of system gain under interference
And thus protect the high priority traffic to pass
With No BER.
Contents
1+1 HSB
In the transmit direction: The service signal is transmitted to the main ODU and the standby ODU after traversing the cross-connect board. Then, the service signal is transmitted to the antenna through the hybrid coupler. In normal cases, the standby ODU is muted. After the switching, the main ODU is muted and the standby ODU starts to work.
In the receive direction: The service signal received at the antenna is transmitted to the cross-connect board through the main ODU and the standby ODU. The cross-connect board selects the signal transmitted from the main IF board.
If faults of different types occur, service signals may be transmitted or received through different ODUs.
Cross-connect board
Service board
Muted
Muted
1+1 HSB configuration: In normal cases, the standby ODU is muted and does not transmit RF signals. The cross-connect board selects the service signal transmitted from the main IF board.
The signal transmitted from the service board is sent to the main IF board and the standby IF board, and then to the main ODU and the standby ODU respectively. Only the main ODU transmits the RF signal to the hybrid coupler. The antenna then transmits the RF signal.
The RF signal received at the antenna is sent to the main ODU and the standby ODU, after traversing the hybrid coupler. The RF signal then is sent to the main IF board and the standby IF board, which transmit the RF signal to the cross-connect board. The cross-connect board selects the service signal transmitted from the main IF board and then transmits the signal to the service board.
After the HSB switching, the main ODU is muted and the standby ODU starts to transmit signals. The cross-connect board selects the service signal transmitted from the standby IF board.
1+1 SD
Muted
Muted
In the case of the IDU 950, the main IF board and the standby IF board must be installed in paired slots.
In the receive direction: The main IF board and the standby IF board transmit the received service signal to each other. When a fault occurs on the main channel or the quality of the service on the main channel declines, the main ODU selects the service signal transmitted from the standby IF board (HSM switching).
1+1 SD configuration: In normal cases, the standby ODU is muted and does not transmit RF signals. The cross-connect board selects the service signal transmitted from the main IF board.
The service signal transmitted from the service board is transmitted to the main IF board and the standby IF board, after traversing the cross-connect board. The main IF board and the standby IF board then transmit the service signal to the main ODU and the standby ODU. Only the main ODU transmits the RF signal through the antenna.
The two antennas receive the RF signal and then transmits the RF signal to the main ODU and the standby ODU respectively. The main ODU and the standby ODU transmit the RF signal to the main IF board and the standby IF board respectively. After that, the signal is transmitted to the cross-connect board. The cross-connect board selects and transmits the service signal transmitted from the main IF board to the service board.
The two IF boards transmit the received service signal to each other. In normal cases, one IF board receives the service signal on the local board.
After the 1+1 SD HSM switching, the main IF board receives the service signal transmitted from the IF board in its paired slot.
After the HSM switching, the signal flow in the receive direction is as follows: standby antenna -> standby ODU -> standby IF board -> main IF board -> cross-connect board -> service board.
1+1 FD
tf2
rf2
tf1
rf1
Compared with the 1+1 SD protection, the 1+1 FD protection uses two frequencies.
The main ODU and the standby ODU both transmit signals.
1+1 FD configuration: In normal cases, the main ODU and the standby ODU both transmit RF signals on different frequencies. The cross-connect board selects the service signal transmitted from the main IF board.
The service signal transmitted from the service board is sent to the main IF board the standby IF board, after traversing the cross-connect board. The main IF and the standby IF board then transmit the signal to the main ODU and the standby ODU respectively. The main ODU and the standby ODU transmit RF signal on different frequencies, which are combined by the hybrid coupler. The RF signal is then transmitted through the antenna.
The RF signal received at the antenna is separated by the hybrid coupler into RF signals on different frequencies. The signals on different frequencies are transmitted to the main ODU and the standby ODU. After the RF signals are converted into IF signals, the IF signals are transmitted to the IF boards and then to the cross-connect board. The cross-connect board selects the service signal transmitted from the main IF board and then transmits the service signal to the service board.
The two IF boards transmit the service signal to each other. In normal cases, one IF board receives the service signal on the local board.
After the 1+1 FD HSM switching, the main IF board selects the service signal transmitted from the IF board in its paired slot. After the
HSM switching, the signal flow in the receive direction is as follows: antenna -> hybrid coupler -> standby ODU -> standby IF board -> main IF board -> cross-connect board -> service board.
After the 1+1 FD HSB switching, the cross-connect board selects the service signal transmitted from the standby IF board and the standby IF board selects the service signal on the local board.
Comparison Between the 1+1 HSB, 1+1 SD, and 1+1 FD — Traditional Microwave
HSB (Switching on the Equipment Side )
HSM (Switching on the Channel Side )
1+1 HSB
Switching condition
Automatic switching: hardware fault of the IF board, hardware fault of the ODU, remote fault indication, and loss of microwave frames Switching triggered by external commands: lockout of protection, forced switching, manual switching, and clear switching
Automatic switching: loss of microwave signals, loss of microwave frames, bit errors in microwave frames, and forced selection of the service signal from the IF board in the paired slot triggered by the HSB switching Switching triggered by external commands: commands of forcibly selecting the service signal from the IF board in the paired slot and clearing the forced selection
Slot restriction
The main IF board and the standby IF board need not be installed in the paired slots.
In the case of the IDU 620, the main IF board and the standby IF board must be installed in the paired slots.
Switching time
< 500 ms The software and the hardware perform the switching action.
The hardware performs the automatic switching action quickly. During the switching process, bit errors do not occur.
Revertive switching
The revertive mode and the non-revertive mode are supported. The wait-to-restore (WTR) time can be set to 5 to 12 minutes.
Regardless of whether the switching is set to the revertive mode or the non-revertive mode, the IF board attempts to perform a revertive switching action every two minutes after the HSM switching.
Switching mode
Single-ended switching
Single-ended switching
Revertive mode: When an NE is in the switching state, the NE releases the switching and enables the former working channel to return to the normal state some time after the former working channel is restored to normal. The period from the time the former working channel is restored to normal to the time the NE releases the switching is called the WTR time. To prevent frequent switching events due to an unstable working channel, it is recommended that you set the WTR time to 5 to 12 minutes.
Non-revertive mode: The NE that is in the switching state remains the state of the former working channel unchanged even though the former working channel is restored to normal unless another switching occurs.
Contents
Microwave Frequency Planning
Co-channel interference:
When the interfering signal has the same frequency as the interfered signal, the interference is called co-channel interference.
F1 (transmitted signal) = F2 (interfering signal)
F1
F2
FREQ
RX1
Microwave Frequency Planning
Adjacent channel interference:
When the central frequency of the interfering signal falls in an adjacent channel of the main transmitted signal, the interference is called adjacent channel interference.
F1 (transmitted signal) and F2 (interfering signal) are overlapped.
F1
F2
FREQ
RX1
Microwave Interference Analysis
Adjacent links of the same BTS
Other stations on a chain network
Networks of the other carriers
Other possible interference sources, such as radio stations, radar stations, or other equipment
Poor grounding or electrostatic shielding of microwave equipment
Cause of co-channel interference and adjacent channel interference:
The angle between two adjacent links of the same BTS is smaller than 90 degrees
Single-channel configuration
Short-haul chain network topology
Examples of co-channel interference in microwave transmission:
Case 1: Interference caused when the antenna beam width is large and the included angle between links is small. The signals transmitted from site A to site B interfere with the signals received by site B from site C. Similarly, the signals transmitted from site C to site B also interfere with the signals received by site B from site A.
80 Deg.
Site A
Site B
Site C
Case 2: Front-back interference is caused by a poor front-back ratio of antennas. The signals transmitted from site X interfere with the signals received by site Y from site Z. Similarly, the signals transmitted from site Y to site X also interfere with the signals received by site Z from site Y.
Site X
Site Z
Site Y
Case 3: Overreach interference. The signals transmitted from site A to site B interfere with the signals received by site D from site C. Similarly, the signals transmitted from site D to site C interfere with the signals received by site A from site B.
A
B
C
D
F1
F2
F1
Target C/I ratio related to microwave interference:
The target C/I ratio indicates the ability of a microwave receiver to tolerate radio interference from the same band, that is, the ability to tolerate co-channel or adjacent channel interference.
F1
F2
FREQ
RX1
Requirements on the C/I Ratio related to microwave interference:
The C/I ratio on the input port of a microwave radio receiver should be equal to or higher than the target C/I ratio, so that the receiver can attain the threshold-to-interference (T/I) ratio.
The lower requirements on the target C/I ratio on the input port of a microwave radio receiver, the stronger ability of the receiver to resist interference.
Definition of the T/I ratio related to microwave interference:
The T/I ratio defines interfering signal influence on the interfered radio receiver, that is, a radio receiver sensitivity to interfering signals.
When the static threshold of a radio receiver is known, the received signals can manually fade till…

3- microwave and radio

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