Contents
6.1 Summary of Contributions and Discussions . . . 110 6.2 Suggestions for Future Work . . . 111
6.1 Summary of Contributions and Discussions
In this thesis, we address issues concerning modeling and analysis of interference in an asyn- chronous environment. We propose models and methods to quantify the asynchronous interfer- ence. Moreover, this thesis discusses an crucial issue of interference management in heteroge- neous/overlaid wireless networks. This chapter presents the summary of the thesis and also dis- cusses some of the possible future directions of extension of the research works reported in this thesis. The main contributions of this thesis are summarized in Section 6.1 and possible future extension of the work are outlined in Section 6.2.
6.1 Summary of Contributions and Discussions
In this section, we briefly summarize and discuss our contributions and findings during this thesis work. This thesis presents :
4 Comprehensive review of Various Aspects of Interference in an Asynchronous Environment:
Issues related to interference in un-coordinated networks have been discussed in detail. Vari- ous available models/approaches to quantify the interference have been discussed thoroughly and their shortcomings while addressing interference in asynchronous environment have been pointed out. Some asynchronous interference modeling aspects which are not well addressed in the literature have also been discussed.
4 Outage Analysis of an Asynchronous network Using Proposed Model :
We proposed a model to calculate the effective overlap experienced by the bit of desired frame due to the bit(s) of interfering frame. Also, we introduced a metricEINRto quantify ratio of the desired energy to interference energy plus noise spectral density ratio. Effective number of interferers, taking MAC protocol into account, is calculated. Using theEINRmetric, outage performance has been analyzed to observe the effects of i.n.i.d. interferes on wireless network performance. Apart from outage probability, some other parameters such as performance of individual node in terms of total successfully received bits, total successful receptions throughout the network, average interference energy are also investigated. To observe the effect of antenna height on network performance in an interference limited environment, some simulation results has been presented.
6.2 Suggestions for Future Work
4 BER Analysis of an Asynchronous network :
In order to quantify the effects of interference on network performance, we have evaluated the BER in the presence of i.n.i.d. interferers employing the BPSK scheme. A method is proposed to find the (partial) overlap and index of bit(s) of interfering frame. To calculate the BER, overlap of frames is addressed carefully using the proposed method. Pdf of effective signed fractional overlap variable is calculated taking partial overlap into account. Using an amplitude metric approach, pdf of resultant amplitude of effective interference has been calculated. By applying appropriate approximations, closed form expression for the BER is also derived. Along with BER variation w.r.t number of i.n.i.d. interferers, several other performance measures have also been investigated, such as, variation of number of successfully received bits by a single user and average variance sum w.r.t. i.n.i.d. interferers as well as interference range factor. Average bit success rate and interference variance sum are investigated w.r.t. interference range factor. Inconsequentialness of phase terms, associated with interfering signals, in the presence of large number of interferers are also pointed out.
4 Investigation of Interference Management methods for Heterogeneous/Overlaid networks :
In this part of work, we have discussed management of interference in heterogeneous/overlaid wireless networks. Some existing methods of interference management have been investi- gated. Interference management by subband allocation has been discussed in detail. For il- lustrating the concept of interference management in an overlaid network, a two-tier OFDMA based femtocell-cellular network combination has been taken as an example. An analytical framework has been proposed to find the optimum subband for communication purposes in femtocells.
6.2 Suggestions for Future Work
In this thesis we have addressed some of the basic issues related to interference analysis and management for multi-user environment. We classify some possible directions in which the present work can be extended into two parts, as outlined below:
a) Direct Extension of the Current Work :
While carrying out the research work presented in this thesis, we have taken some assumptions
6.2 Suggestions for Future Work
in order to reduce the computational complexities. Replacing those assumptions with more practical constraints may bring some additional insight to the system performance. Therefore, the work presented here can be directly extended by incorporating practical conditions in place of assumptions taken. This sub-section talks about some such possibilities :
. In outage analysis, to calculate the mean and variance of sum of log normal RVs, Wilkinson’s approach has been used. Some other robust methods such as Schwartz and Yeh’s, cumulants Matching Method may be used to obtain better accuracy. However, it may incur calculation burden.
. For BER calculations, system is assumed to be utilizing BPSK modulation scheme.
Work can be extended for MPSK schemes. It can also be extended for other modulation schemes as well.
.An uncoded system is assumed for this work. Study of coded systems may be a possible area of extension.
. BER and subband selection investigations may be extended by including shadow effects for a better characterization of fading environment.
. Users with unequal frame lengths and effects of ACI may be taken into account for modeling of a relatively general scenario.
b) Extension in Other Possible Directions :
Apart from the possibilities described above, some other potential directions in which, this work can be extended are as follows :
. Recent literature shows that various interactions among independent nodes, interference and resource conflict scenarios in wireless networks may be efficiently modeled as a game by using a set of tools offered by game theory. We envisage that analysing interference limited networks with help of game theory may be an efficient and interesting way to model complex scenarios.
.The analysis presented in this thesis does not consider any user cooperation. Interference analysis of a co-operative system can also be carried out.