1. 12th WSEAS International Conference on COMMUNICATIONS, Heraklion, Greece, July 23-25, 2008
CONTROL SYSTEM TO REDUCE ADJACENT
INTERFERENCE IN BASE STATIONS
EDGAR ALEJANDRO ANDRADE GONZÁLEZ
SILVIA RODRÍGUEZ CARPIO
MARIO REYES AYALA
JOSÉ ALFREDO TIRADO MÉNDEZ
Electronic Department
Metropolitan Autonomous University-Azcapotzalco
Ave. St Pablo # 180, Col. Reynosa Tamaulipas, México City, México
CINVESTAV-IPN
MÉXICO
Abstract: - This paper shows a control system to reduce adjacent interference in a cellular environment keeping the
longest distance between channels used by the handsets. This control system change dynamically the resources
(forward and reverse channel) allocated to all the users of the cellular system in order to maintain less interference in
the channels (adjacent interference).
Key-Words: - Cellular, Adjacent Interference, Channel, Base Station, Dynamical Allocation.
1 Introduction It is important to have prototype tools to emulate the
The big growing of the wireless devices in cellular communication systems for educational
radiocommunication systems and high transmission application in order to improve the knowledge process
rates gives as a result the need to do an optimal of the communication system analysis.
management of the spectrum and also gives as a
consequence that the electronic devices operates with 2 Design of the control system
wide bandwidth. The control system consists in three blocks: the
In the cellular systems, several unwanted factors Personal Computer, the microcontroller and the logic
appear like fading, co-channel interference, adjacent- for the control of the VCOs (voltage control
channel interference, etc. The use of a limited oscillator). The VCOs has a bandwidth range from 760
spectrum in the communication system makes more MHz to 870 MHz.
difficult to management it maintaining the less
interference between the users.
One of the worst unwanted effects is the adjacent
channel interference, which is generated when a signal
interferes the bandwidth of another channel nearby.
There are several techniques to reduce adjacent
channel interference, like filters with high order, using
the feedforward structure in power amplifiers,
modulation techniques, etc. [1][2].
In this paper, we show an algorithm to reduce the
adjacent channel interference in the base station Fig. 1 Control system
maintaining the longest distance between channels
anytime. This control system allocates the channels to In the personal computer, the algorithm for the
the users maintaining the best conditions into the base allocation of the frequencies is programmed. Also, this
station to gives a good performance reducing the software application establishes the communication
adjacent channel interference reassigned all the with the microcontroller ATMEGA8535 through the
channel of the users. With this application the students serial port.
can check the management of the channels for the The information interchanging between them are
users while they are in moving into a cell. related with the code for the users (consist of three
ISSN: 1790-5117 456 ISBN: 978-960-6766-84-8

2. 12th WSEAS International Conference on COMMUNICATIONS, Heraklion, Greece, July 23-25, 2008
bits), the code for the channels (consist of three bits) communication service. Then, after that the system
and the flags for the disconnection or establishment of analyzes if there are channels available or not; if there
the service for a specific user (one bit), with a specific is at least one of them, then it proceeds to allocate the
structure of the data as we can see in the frame below. channel with the longest distance between that user
and the others in the system.
The second task is if the user wants to finish the
communication, in that case, the channel assigned to
the user is released in order to be used by other user in
the next establish of service.
3.1 Algorithm to establish the communication
Fig. 2 Data Frame
After we check that there are available channels in
the system, it proceeds to assign the channel which has
The microcontroller has three ports, one port for the maximum distance between the channels occupied
serial communication to receive the data to the and the new one (request).
configuration of the frequencies depending of the user To achieve this goal, we have a data base of the
code and the channel code, one port to select the user channels with the maximum distance between them
and the channel transmit the resulting code to the and we select the channel according to the availability
codecs and finally, one port for the gain control of the in that moment. The way that the channels are
power amplifiers in the RF transmission block of the allocated to the users (for example for eight users) is
base station. This last function was not showed in this showed in the table 1 and table 2.
paper.
The last block consists in logic for decoding the user
and channel and also using a Digital to Analog Order of Channel
Converter (DAC) to choose the channel desired in the Allocation
VCO for a specific user. 1 1
2 8
3 Design of the Algorithm 3 4
We show the algorithm explanation with eight users 4 6
and eight different channels. The sequence of the
process to allocate channels to the users is based in the
5 2
following flow chart. 6 7
7 5
8 3
Table 1 Allocation showing the maximum
distance between channels
Where:
Channels Frequencies
MHz
1 760
2 775.7
3 791.4
4 807.1
Fig. 3 Algorithm general 5 822.8
6 838.5
The process to initiate the choosing of the channels
of the users, it starts when there is an event of a user, 7 854.2
which asks for the resources of the system in order to 8 870
establish the communication or leave the Table 2 Channels frequencies
ISSN: 1790-5117 457 ISBN: 978-960-6766-84-8

3. 12th WSEAS International Conference on COMMUNICATIONS, Heraklion, Greece, July 23-25, 2008
3.1 Algorithm to finish the communication
This algorithm frees the channel of the user selected,
but only if the user is using the last channel assigned;
this means that it is not necessary to reassign all the
channels of the rest of the users that are using
resources of the system, because all of them maintain
the longest distance between themselves [3].
In general way, when a user wants to leave the
channel assigned to him; and this user it is not the last
one (assigned), then we have to rearranged all of the
channels allocated to the users occupying the place of
the user disconnected in order as the users enter to the
system to ask for a channel after the user involve,
giving as result, the channel allocation showing the
longest distance between themselves [3].
4 Conclusion
This system control for the management of the
resources of the system (reverse channels and forward
channels) shows a dynamical control, maintaining all
the time the users arrive asking for resources or
leaving the communication, the longest distance
between their frequencies assigned (channels)
reducing the adjacent channel interference. We are
working in control of the gain in the amplifiers (low
noise amplifier and power amplifier) with the same
system using the same frame but with the 7th bit of the
frame; we use this prototype for educational purposes.
Finally, this management of the channels improves the
performance of the duplexer in FDM communication
systems.
References:
[1] P. García, A. Valdovinos et all, “Método de
Equilibrado basado en Algoritmos Genéticos e un
Esquema de Linealización Feedforward” Spain
[2] H. Hammuda, “Cellular Mobile Radio Systems:
Designing Systems for Capacity Optimization”, 1997
[3] S. Rodríguez, “Bloque de Radiofrecuencia para
Transmisión de una Estación Base”, Thesis, México,
2008
ISSN: 1790-5117 458 ISBN: 978-960-6766-84-8