Performance Analysis Of LAA And Wi-Fi Coexistence Fairness In The Unlicensed Bands

Long term evolution-licensed assisted access(LTE-LAA)is the second variant of LTE-unlicensed that has been standardized by the 3GPP in Rel-13.Due to the fact that LTE-LAA combines the usage of licensed and unlicensed band when coexisting with Wi-Fi.Therefore,it is more adaptable and profitable than the LTE-U version of the LTE-U forum,Licensed assisted access uses the licensed and unlicensed band when coexisting with Wi-Fi owing to the fact that listen before talk(LBT)mechanism uses the technics of listen before transmission of data during the OFF period of LAA and as a results is the ON period for Wi-Fi.In addition,listen before talk mechanism currently adheres to the requirements of frame based equipment(FBE)and load based equipment(LBE)coexisting scheme.Recently the main challenge of realizing LTE-LAA coexisting with Wi-Fi in the licensed and unlicensed band is that it leads the performance of Wi-Fi to starvation.Meanwhile,Wi-Fi does not get the same opportunity to access the channel as LTE does,for example,Wi-Fi can wait for two cycles to access the channel because during those two cycle LAA occupy the channel,every time one of the contending equipment wants to access the channel,it have to listen weather the channel is idle before it send its data.Due to the fact that licensed assisted access equipment contention window are small compared to that of Wi-Fi;therefore LAA access the channel for many times than Wi-Fi.As a result this affects Wi-Fi,because Wi-Fi will experience many back off clear channel assessment,In addition it makes the coexistence fairness poor between the two heterogeneous equipment.In this thesis,we assess the fairness improvement of LTE-LAA when Wi-Fi is coexisting with LAA equipment;namely frame based equipment and load based equipment mechanisms(FBE and LBE respectively)in the unlicensed band.By means of mat lab programming language,we analyze the channel access opportunity and fairness index for better readings.Furthermore,we do an adjustment of all licensed assisted access equipment so that to make all the equipment that are contending to access the channel to do back off as Wi-Fi does and for the sake of lowering the time delay that all the equipment have to go through.The first adjustment is a modification of the Frame Based Equipment(M-FBE)whereby we have done the analysis by removing the 5%idle period of Frame Based Equipment transmission time.Consequently,the M-FBE simulation results have demonstrated that,with M-FBE the coexistence fairness is improved two times fairer compared to the results obtained when the 5%idle period of the frame based equipment transmission period is present.Furthermore,The fact that we can still adjust or modify one of the two(LBE&FBE)scheme of listen before talk 3GPP mechanism according to the most advantageous,meanwhile in a way that can help in improving the fairness when both frame-based equipment,load based equipment share the same resources with Wi-Fi or among themselves.In short,in this study we have used the frame-based equipment modified to compare the simulation results of when the frame-based equipment only undergoes the back off mechanism and when it still undergoes back off mechanism but without the 5%idle period.Below are some of the advantage of frame-based equipment coexisting with Wi-Fi or another licensed assisted access.The fairness is improved to a maximum value specifically 90%,compared to when it still apply the 5%idle period and the smallest fairness index lies on 50%it does not go below that minimum value while with the frame based equipment undergoes the back off mechanism with 5%idle period fairness goes below 50%.So it have solved the problem of FBE contention window meanwhile the starvation when do back off,with modified frame-based equipment without 5%idle period,the results is not very much affected when the q values is small,here we have run an example of q1 equals 4 and the results was good.Besides there is Disadvantage associated with Modified Frame Based Equipment such as:At first the frame-based equipment undergoes the back off scheme it affects its working principle since it was not designed to do so,as we have seen in simulation results,frame based equipment suffer the same starvation as Wi-Fi,It affect the channel efficiency;meanwhile,frame based equipment is slowed down by adding the 5%fixed of its transmission time,in addition,since the frame based equipment will be experiencing the back off time it will delay the process more.And this is for frame based equipment not to collide with load based equipment and Wi-Fi and for Frame based equipment to not always be dominated by LBE and Wi-Fi as now all equipment experience the same delay but for Wi-Fi it add 9s of DIFS which makes FBE to come last and frame based equipment experiencing new working principle that slow it down so all this makes load based equipment to come first which means that its contention window is small compared to that of Wi-Fi and FBE.The second modification is of the LBE whereby we explored an assumption of when one of the contending equipment;namely Wi-Fi and LAA equipment have not finished their data transmission and yet their transmission time are over.Therefore we set a condition that Wi-Fi or LAA equipment can continue to send within the back of time but due to the fact that we have to keep order and avoid the collisions the next equipment resume that same time in the next frame if the next equipment do not have a lot of data to transmit.Moreover,in case the next equipment also have a lot of data to send,it will keep the process.Meanwhile,if the situation becomes the opposite,the system will keep extending that time until it gets the opportunity to resume it.As a results,with this second modification the coexistence fairness is improved to about three times and fairer.In addition,the second modification namely load based equipment is quite stable compared to previous mechanism of modified frame based equipment as it's fairness varies between 80%and 85%range according to the results obtained by simulating the total and average Jain's fairness index.In short,the fact that the fixed frame period of modified frame based equipment in the second contribution is not variable or is constant it does not mean that we cannot pair it or put it in hybrid with the rest of the equipment namely Wi-Fi and M-LBE.Therefore we still can varies in between of each equipment competing to access the channel namely LAA equipment using frame based equipment and load based equipment and Wi-Fi,Furthermore,there is more advantages that goes with the modification such as:the way it reduces the time delays of the system,In case the send of information of one equipment among the competing equipment finish before the estimated time the remaining time will be used to the next frame of the different equipment that have a lot of information to send.As a result,this will ensure the stability and it will keep the fairness above 80%a throughput fairness.In addition the fairness will not go below 80%as it varies between(80-85)percent as the simulation results have revealed.And It reduces the loss of information(packets)curried by the equipment and there will be no collision,since both load based equipment and Wi-Fi are allowed to send all the packets even when its assigned time session is over.Moreover,there is Disadvantage associated with modified Load Based Equipment because,we were only able to varies modified load based equipment and Wi-Fi while frame based equipment was fixed and which might hinder its transmission well fair as it will not be allowed to extend the transmission period when in need or resume its transmission time so that it can be added to the next frame of a different competent.It does not contribute much to our target of time delay reduction for better fairness,meanwhile,when in hybrid with the remaining equipment it draws back the total fairness and it does not work mutually with the M-LBE and Wi-Fi because of fixed frame period thus,it does not adjust time according to the load.The third modification consist of a time variation.Whereby we have made the transmission time variable of modified frame based equipment,and we have given it a name of continuous frame based equipment(C-FBE).Owing to the fact that it is not fixed like modified frame based equipment,is different from all the previous modification where the FBE transmission time is fixed.Therefore,with the third modification the coexistence fairness is improved to about four times.In addition,the third modification namely continuous frame based equipment is quite stable compared to both previous mechanism of modified frame based equipment and modified load based equipment respectively as its fairness varies between 85%and 98%range.According to the results obtained by simulating the total and average Jain's fairness index explained in a Comparison of all proposed scheme M-FBE/M-LBE and C-FBE,in a hybrid,As a result,C-FBE is the best mechanism as it keeps the coexistence fairness stable and on a maximum value not achieved by any other mechanism among the three,and it solve the problem of the channel efficiency that was raised by theM-LBE explained in the same comparison figure with C-FBE.Which in turn solve the problem of coexistence fairness that have raised by M-FBE represented by in the same comparing figure with C-FBE and M-LBE.Meanwhile,M-FBE frame based equipment is slowed down by addition of the 5%fixed of its transmission time,in addition,since the frame based equipment will be experiencing the back off time it will delay the process more.And this is for frame based equipment not to collide with load based equipment and Wi-Fi and for Frame based equipment to not always be dominated by LBE and Wi-Fi as now all equipment experience the same delay but for Wi-Fi it add 9s of DIFS which makes FBE to come last and frame based equipment experiencing new working principle that slow it down so all this makes load based equipment to come first it's contention window is small compared to that of Wi-Fi and FBE.In summary,we have done a comparative simulation of all licensed assisted access listen before talk based mechanism,namely;modified frame based equipment,and modified load based equipment and continuous frame based equipment.The analysis have shown how the fairness improves only with maximum values of q[LBE,FBE]meanwhile with q minimum fairness goes to the value under the minimum of Jain's fairness which is 50%when two or more than two equipment are sharing the same resources.Therefore,that is where the use of modified frame based equipment benefit,In addition with the same working principles as that of Load Based Equipment except that the transmission time of frame based equipment is fixed while the transmission time of load based equipment values according to the load,the difference between the two Frame Based Equipment adjustment is that we Implemented the proposed mechanism without the five percent of transmission time idle period,Briefly all the mechanisms improves the fairness even when FBE and LBE q values are on their min values,as the experimental results have proved.The fairness can be assured for above forty percent above normal when using the modified frame Based equipment as our concerns in this thesis we wanted to raise the fairness to a point where it can be stable and do not varies within the range of below minimum of fifty percent.In conclusion,after the analysis,it was concluded that all the mentioned LBT based coexistence scheme(M-FBE,M-LBE and C-FBE)leads to fairness enhancement between Wi-Fi and LAA.In addition the C-FBE mechanism goes far along to keep the coexistence fairness stable,either the fixed back off value is on its minimum or is on its maximum value.As a results the throughput of C-FBE is the highest,followed by the M-LBE and finally the M-FBE according to the comparative results obtained using mat lab to simulate the average and total fairness.