Microsoft Word CellBreathing

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Cell Breathing and Cell Capacity in CDMA: Algorithm & Evaluation 
Ihsan UlHaq
1
, Adnan Shafiq
2
, Khawaja M. Yahya
2
 
1
Deptt of Electrical and Computer Engineering, Faculty of Engineering, University of 
Porto, Portugal. 
2
Deptt of Electrical Engineering, NWFP University of Engineering & Technology 
Peshawar, Pakistan 
[e-mail]
,
[e-mail], 
[e-mail]
 
Abstract. The aim of this article is to present an algorithm for CDMA based 
third generation cellular networks. The algorithm helps to prevent Cell 
Breathing and thereby increases the Cell Capacity in terms of density of 
Mobile Stations (User Equipment), as the Mobile Stations at the edge of cell 
will not be disconnected due to Cell Breathing. The algorithm also facilitates in 
Proactive Handover as the codes are made available for the MSs in advance. 
So this algorithm can be used to make CDMA system more robust to 
interference. Simulation study has been performed to verify the proposed 
algorithm. 
Keywords: Cell Breathing, Network Capacity 
1.
 
Introduction 
Interference is a major factor that limits the coverage area of CDMA based networks and 
as a consequence the capacity in terms of density of MS in a Cell. In order to keep the 
interference at a minimum it is important to have a precise and fast power control [Jalali 
2002, Sumit 2004, Qualcomm]. Users that are further away from Node B (BTS in case of 
CDMA2000) have to send with more power than those closer to Node B, as the signal 
gets weaker the further it has to travel. An increase in interference normally occurs when 
multiple users enters a cell which in turn requires that the existing users at the edge of the 
cell to further increase their transmit power. If the users at the edge (border users) do not 
have the capacity to transmit at a power that will overcome the noise floor, the user will 
be disconnected. As a consequence, the coverage area of the cell is reduced, as most 
distant users (border users) cannot communicate with the Node B. This phenomenon is 
called Cell Breathing. 
Our proposed algorithm prevents Cell Breathing especially when multiple active 
users enter the coverage area of a cell, for example traveling in a vehicle like a train or a 
bus. The users will require simultaneous handovers to the target Node-B. We term this 
simultaneous handovers as “Group Handover”. These simultaneous multiple users will 
increase the noise floor thus requiring the border users to further increase their transmit 
power, which may not be further possible and thus result in their disconnection from the 
network. In order to continue all ongoing connections as well as to facilitate successful 
Group Handover to the target Node B, proper planning of resources is required. The goal 
of our proposed work is to reduce the interference to a level that will allow to continue 
all existing connection to the Node B and to facilitate successful Group Handover. 

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In this article a resource allocation algorithm based on location information is 
proposed for Group handover. It uses the location information of users to allocate or free 
resources in the target cell in advance, while keeping the interference level with in the 
threshold values. The algorithm prevents Cell Breathing thereby increasing network 
capacity and coverage. By preventing Cell Breathing, the users at the edge of the cell 
remain connected to the system and thus Quality of Service in terms of connectivity is 
provided to the users. 
The balance of this article is organized as follow. In Section 2, related work to 
prevent cell breathing and the issues related to these mechanisms is presented. Section 3 
elaborates the procedure to assign variable lengths codes to users while section 4 
presents our proposed solution based on location information. Section 5 explains the 
simulation to verify the algorithm and Section 6 provides conclusions.