003. Radio Features.pdf

FlexiPacket ODU Features

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© 2012 Nokia Siemens Networks 1

Content

1 FlexiPacket MultiRadio Features 3

1.1 Main Features 3

1.2 Adaptive Code and Modulation (ACM) 4

1.3 ATPC 7

1.4 Modem with XPIC (Cross Polar Interface Canceller) 9

1.5 Loopbacks 10

1.6 Quality of Service 12

1.7 Modulation driven service add/drop (formerly known as “E1/T1 priorization 13

1.8 Header compression 14

1.9 Ethernet Port Rapid Shutdown 16

1.10 Performance Monitoring 17

1.11 Synchronization and Clock Recovery 23

1.12 Security features 30

1.13 FlexiPacket MultiRadio Management: General Information 31

1.14 FlexiPacket MultiRadio License: Introduction 35



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1.2 Adaptive Code and Modulation (ACM)

ACM allows operators to improve link utilization by making high capacity data transmission reliable. ACM changes code and modulation according to the link quality in the same channel bandwidth.

Adaptive Code and Modulation refers to the automatic modulation adjustment that a wireless system can perform to prevent weather related fading from disrupting communication on the link.

When severe weather conditions, such as heavy rain, affect the transmission and receipt of data over the wireless network, the radio system automatically changes the modulation, so that non-real time data-based applications may be affected by signal degradation, but real-time applications will run smoothly and continuously.

Since communication signals are modulated, varying the modulation also varies the amount of bits that are transferred per signal, thus enabling higher throughputs or better spectral efficiencies. It should be noted that when using a higher modulation technique better Signal-to-Noise Ratios (SNR) are needed to overcome interference and maintain a tolerable BER (Bit Error Ratio) level.

Based on the channel's condition, the ACM allows the system to choose the best modulation in order to overcome fading and other interference.

The algorithm uses the highest possible modulation in accordance with link quality degradation.

The switch from a modulation scheme to another modulation scheme takes place according to the "Signal/ Mean Square Error" (S/MSE) value. The ACM thresholds are listed in Fig. 2.

For example, on a clear day, transmit and receive data capacity can be 350 Mbit/s, using 256 QAM modulation. When the weather becomes overcast and stormy, the ACM algorithm changes the modulation to 64 QAM and the system transmits at 260 Mbit/s.

ACM is extremely quick and the modulation switchover is implemented using an Errorless and Hitless algorithm. ACM allows to maximize the spectrum usage and to enable the increased capacity over a given bandwidth.

Switchover has the possibility of stepping up or down through all the modulation schemes covered from 256 QAM down to 4 QAM, and back up all the modulations in between. This guarantees that the link will operate at the highest possible modulation at any time.


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• More Capacity by increasing the Modulation Level

• Engineering the hop for the average capacity

• Transmitting the peak for most of the time (99,99%)

• Service aware Radio: different QoS for different traffic

• TDM Traffic with the same QoS of TDM radio (ie: 5minute/year

unavailability)

• Reuse of installed antennas

Same Antennas

More capacity over the existing bandwidth

Same availability

Time

Link

Capacity

25 min/year

52 min/year

5 min/year

Fig. 1 ACM for traffing growing

The available profiles numbers, corresponding to the available modulations are:

1 = 4 QAM

2= 16 QAM

3= 32 QAM

4= 64 QAM

5 = 128 QAM

6 = 256 QAM


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Fig. 2 ACM thresholds

1.2.1 Configurable minimum modulation mode

Adaptive Code Modulation works between a max Tx Profile and a minimum one to counteract fading.

Lowest Tx Profile and the Highest Tx Profile are settable.

In Rx side the Modulation scheme automatically changes according to the Modulation scheme used in Tx side.


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1.3 ATPC

ATPC (Automatic Transmit Power Control) controls the far-end transmit power level in order to keep the receive signal level above a certain user-defined threshold level in accordance with the particular modulation method and capacity being used.

ATPC is designed to counteract fading speed of 50dB/s tuning Tx power in the Tx power range of 25dB.

FlexiPacket ATPC Settings are shown in Fig. 3

Fig. 3 FlexiPacket ATPC Settings

Only the power level driven operation mode has been implemented.


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1.4 Modem with XPIC (Cross Polar Interface Canceller)

The XPIC is used in co-channel configurations.

Co-channel operation with high level modulation schemes requires very high cross-polarization discrimination (XPD).

Modern radio relay antennas meet the XPD requirements at least under ideal propagation conditions; nevertheless cross-polarization interference (XPI) between orthogonally arranged channels may increase under particular conditions such as rainfall or multipath propagation.

To counteract these phenomena a powerful cross-polarization interference canceller has been fit into the demodulator.

Since the interference effects are time variable, the XPIC device structure is adaptive, consisting also of transversal filter.

At transmit side, it is not requested neither the common use for the V and H channels of a single L.O. nor the synchronization of the two used oscillators.

There is also no strict requirement for clock synchronization at transmit side.

At receive side, beside the exchange of the received data signals at IF level, the only interconnection between vertical and horizontal channel is the L.O. synchronization of the receivers and no additional clock synchronization of the demodulators is necessary.

Another advantage of this concept is the independence of the XPIC operation from the lock-in state of the carrier recovery being the carrier frequencies of the interfering signal and the compensation signal identical at the adder point.

This greatly improves performances after strong XPI events, since the XPIC can first remove the XPI on the main signal, thus facilitating the subsequent lock-in procedure.


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1.5 Loopbacks

The loopbacks can be:

Local (signal looped back towards the GbE cable),

Remote (signal looped back towards the radio interface).

Not more than one loopback can be enabled at a given time. When a loopback is enabled, the system moves to a "test mode" configuration designed for transmitting back traffic.

The differences between the test and the normal are in the L2 switch configuration. When operating in test mode the auto-learning and filtering functions are disabled; the MAC forwarding table is flushed.

During the entire duration of the loopback the FlexiPacket MultiRadio is not reachable for management. Moreover after loopback has been performed, a file becomes available containing the result of the counters.

These loopbacks are available (see Fig. 4):

LL1: used to test cable connectivity.

RL1: used to remotely test the whole chain.

LL2: RF loopback not involving the diplexer as shown in Fig. 5.

Fig. 4 FlexiPacket Radio loopbacks


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Fig. 5 RF Loopback

Documents

003. Radio Features.pdf