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Basics of GSM Radio Communication and Spectral Efficiency

The analysis shows that to gain an advantage from frequency hopping it is necessary to deploy more than two hopping channels. Frequency hopping can be used to improve the network quality where significant improvements can be achieved. The improvement in network quality depends on the channel occupancy. Published in: VTC ' Pathway to Global Wireless Revolution Cat. Article :. Even if channel hopping temporarily falls into deep fading, it quickly escapes fading, and when resent to increase the probability of success, as shown in Figure 5 , it is the method of hopping within data link levels that changes the carrier frequency regularly within the packet.

However, in this type of channel hopping when the condition of the channel is unknown, changing the channel according to the preset pattern presents a problem, in that it does not consider improving performance for communication. In adaptive channel hopping, the system periodically changes its main operation to avoid interference with other devices. The method avoids considering the channels that are in bad condition to improve the stability and performance of the network.

The blacklist is constantly changing depending on the changing channel conditions. The blacklist is in the form of a bit mask, and each bit is consistent with the 16 channels. Based on this, blacklisted channels are excluded from the order of channel hopping.


The received information on the channel numbers that are in use is kept. In a duplex communication method, as shown in Figure 6 , there is a sender A and a receiver B to inform on the uplink and downlink from the sender to receiver and select the frequency channel as the next hop to use the feedback from uplink. As a different adaptive channel-hopping method, the Received Signal Strength Indicator RSSI is collected, and only the channels that are over the standard are used.

However, while these diverse types of adaptive channel hopping choose good channels depending on their communication status and can improve their performance depending on how much time has passed, the channel status can change into a state where communication is not possible. Adaptive Frequency Hopping AFH 24 is a technique designed to solve interference problems in different wireless technologies that share the 2.

This technique that uses frequencies that are available in the spectrum band. It is implemented as a way to avoid interference. The AFH divides the 2.

The hybrid channel-hopping method mixes the standard channel-hopping method and adaptive channel-hopping method depending on the situation. For all of the 16 channels to communicate, when there are no communication problems for all 16 channels, the general hopping method is used. However, if communication failure occurs, the coordinator collects the status information of the channels and uses only the channel to be used for hopping. Because the coordinator wastes energy and storage space on gathering channel information for adaptive channel hopping, this method is more wasteful than the standard channel-hopping method.

With the hybrid method, it is difficult to change all the channels, making it impractical to use.

If a base station has data to send to multiple users and the wireless channel from the base station to each user undergoes independent fading, multiuser diversity will show a good downlink channel status at a certain time, while others will not. In this case, the base station can maximize the throughput by preferentially serving users who show a good channel state.

Performance Enhancements in a Frequency Hopping GSM Network -

Considering fairness, the order of services among users should be determined and defined as opportunistic scheduling. The radio signals originating from the transmitter each arrive at the receiver antenna with different phases through different paths. The strength of the combined signal may be smaller than the average depending on the phase of the signals passing through the different paths. It may also be bigger. We propose a method to solve this problem using the hopping method in the narrowband.

In this section, we propose a method of finding the optimal number of channels to reduce the chances of a service outage.

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A channel outage leads to unsatisfactory communication service quality due to channel capacity reduction caused by fading and interference during a measured time. To conduct channel hopping, it needs to take place in channels that have a lower value than the channel outage by recognizing the condition of the channels to be selected. This paper attempts to assess the processes of predicting the condition of the channels to be chosen and determining channels available for use in channel hopping by conducting a comparison between the conditions of the channels and channel outage.

Expressing this is the log out verse signal-to-noise ratio SNR. This approach is expressed as a probability considering diversity characteristics that can operate in various kinds of fading channels. To select channels available for use in channel hopping, it is necessary to recognize the condition of the channels to be chosen. This can be conducted by making inferences with the measured conditions of past channels.

The method of inferring the condition of channels to be chosen can be expressed in Eq. If h random is 0, it indicates that the previous channel had no relation in the past, but if it is 1, it indicates that it is in the same condition as a new channel. By using this, changes in the condition of selected channels can be inferred. The method of obtaining the channel capacity of the current k th channel expressed as C k can be defined as shown below in Eq.

Using this, the condition of the kth channel can be found, and communication is impossible if the measured channel capacity C k falls below the data transmission rate. This situation can be expressed by Eq. In adaptive channel hopping, all channels that have a lower value than the channel outage are classified as channels that can communicate while others are not. These channels are excluded from the hopping pattern.

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Channels classified as channels used for channel hopping are combined for hopping. To minimize service outage, it is composed of channels that have a lower value than the channel outage i. The coordinator sequentially arranges each of the 16 channels in order of channel inefficiency from small to large according to the channel state.

Performance Enhancements in a Frequency Hopping GSM Network

Fail N, M indicates the probability that M channels are in the disabled state and N-M indicates the probability that they are not in the disabled state when N number of channels is used. Count b, M can be expressed as N-M , where the channel state is 1 , that is, the sum of impossible channels is denoted by M , and the channel state is 0 , that is, the usable channel minus the sum of the channels that are impossible in the entire channel N.

Count b, M denotes the number of channels in all situations. In this case, the channel state of the channels is a probability of being disabled and a probability of being available. This can be expressed as follows. The coordinator selects channels that were lower than the channel outage threshold in adaptive channel hopping.

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However, when channel outage uses the single lowest channel or all of the channels are used in channel outage lower than the threshold, after a set period of time the condition of the channels will deteriorate and in the case a single channel cannot be used. Therefore, the service outage is not determined by the number of channels but combination of the channel states. If unnecessary channels are use sending data, eventually it will be created where either all of the data cannot be sent or many channels will be used creating channel waste and optimal service for communication can't be provided.

We propose a method of the optimal number of channels and the channel hopping pattern for minimizing service outage in this section. For channel hopping, if many channels are selected and used, because the channel outage for each of the channels is different, combining them can create a number of different probabilities in value. At this point, the combination of channels needs to be lower than the service outage for communication to be possible, and this is expressed as follows.

This method exploits the benefits from FH directly in the allocation process, increasing the overall frequency plan. Available Output Parameters. Network Simulation Results.

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Interaction between Network Quality Parameters. The Simulation Model. Theoretical Handover Modelling. Handover Improvements.