Wireless Communication Assignment: Research on 4G/5G OFDM Cellular Systems
Task: In this wireless communication assignment students are required to research on an article in the area of wireless communication. The research needs to be geared towards the transmission fundamentals with focus on the wireless channels, analysing the performance of wireless networks.
In the downlink, the contemporary cellular communication standard that is 4G makes use of orthogonal frequency division multiplexing. Recently cellular network has adopted 5G as the radio standard but it is much more flexible than the LTE. The system bandwidth is generally separated into various bandwidth orthogonal carriers that are added to form the sub-channels. In orthogonal frequency division multiplexing, some of the key techniques being used are frequency domain scheduling, adaptive modulation, and multiple inputs and different outputs . All these systems are there to improve the overall spectral efficiency. For scheduling, the base station exactly checks with the user to allocate each of the SC. Within AMC, the base station checks modulation and coding scheme for transmitting the SC. To allow each of these, the base checks each user feedback channel state details for SC. The feedback is not only required for the frequency division duplex system but also for the time-division duplexing system. This takes place due to imperfect calibration for receiving and transmission but also for the interference of uplink and downlink. A minimized feedback scheme plays a key role in ensuring that feedback does not overhead the link..
II. Use Of Reduced Feedback Scheme Within The OFDM System
In the OFDM system, threshold-based, best-m, and differential feedback are found to be well-known methods for reducing feedback. In the case of threshold-based feedback, the feedback of individual user is quantized as per single to noise ratio. While in the case of best-m feedback, individual user reports, indices and related rate supporting the highest rates  . On the contrary, the clustering feedback comes up with adjacent SC being ground in clusters, and feedback is provided for the individual cluster.
Differential schemes for feedback make use of some fewer bit values which has only created a difference for reference value and quantity of feedback. Both the standards 4G LTE and 5G system come up with a combination of the above scheme mentioned in the wireless communication assignment . This feedback is given by using a channel quality indicator that highlights that MCS can be easily decoded for the given transmission bandwidth. There are their feedbacks being specified within LTE. In the case of increased feedback, there is an idea of clustering based feedback where a user generally reports to a single CQI. It stands out to be the highest value for MCS which can be collected if anyhow the system bandwidth were given to the user . For providing suport to the frequency domain modeling, two exact schemes can be used like back extra information for supplement and increasing band. In the throughput of wideband feedback has been found . Medium access control is required to widen the feedback. .
The author of the article explored in the wireless communication assignment has provided us with novel and systematic modeling analyses for differential feedback. This kind of monitoring does not exists in literature as per best of present knowledge. There is a need for the development of different methods of approximation. This provides a valuable insight into mathematical insight into the performance of the feedback scheme. It stands out to be an important part of both 4G and 5G networks. This even enables the system designers to carry evaluation and check the ongoing performance scheme on collection of systems. It is done without the restoration of intensive simulation. The author has derived an expression needed for the HLCS feedback scheme required for the case of single user scenario. It comprises of effect for two cases that are large scale fading and small scale fading. The paper provides a complete idea of 4G LTE and 5G standards where the system model being used for motivation.
III. System Model
The author first summarizes the important features of LTE downlink that motivate the system model which describes the next and set up of terminology. A brief comment has been provided for commonalities with 5G technology . It has been found that downlink in LTE come up with a time interval for 10 ms and has 10 subframes. In this, each of the subframes consists of duration for 1 millisecond which comprises two 0.5 millisecond slots. This individual slot comprises seven OFDM symbols found within the normal cycle. Within, the given frequency, the whole sub-system band is separated into various carriers where the individual has bandwidth of frequency 15 kHz. The physical resources completely block comprises of the group for than 12 adjacent carriers that have duration of exactly one slot.
CQI feedback is found to be a 4-bit value that helps in estimating MCS where users can easily decode the given downlink. The given value of CQI is understand by individual from a single quality measurement for the received reference signal.
A. Small and large scale fading
In terms of large and scale fading, herein the author has considered transmission at point to point within the OFDM downlinks that exist between the BS that comes with Nt transmit antennas and receiving antennas . This results in the emergence of ideas and concepts with the use of notations that is simple in comparison to the multi-cell surrounding. The considered model by the author has captured the system aspects that have been illustrated and can be easily tracked as well as develop insights. The system bandwidth can be further segmented into various parts namely the channel models, small scale fading along large scale fadings . In the case of the channel that exists between the BS and the user, wherein the signals experience the frequency selective that considers the Rayleigh distribution feature. It also further considers path loss as well as shown that has been mentioned in the large scale fadings. As far as the scale fading is considered, a circularly symmetric complex with a value of zero mean and variance is considered. It is assumed that traceability is constant over the subbed . It can be justified herein wireless communication assignment that the bandwidth of the sub-band can be composed of coherence bandwidth of the used channel. The fading gains are found to be in between transmitting antennas belonging to BS and varied receiving antennas of the users. As far as large scale fading is considered, the denotations of lognormal RV used modes the fading and is similar to the other sub-bands. The author specifically used various symbols for demonstrating the process, notations, and for referring to the key elements that are using the fading process.
IV. Numerical Results
The author has analyzed the results based on the key findings of the paper. In the case of multi-cell, a hexagonal cellular outline has been considered with its radium and co-channel in emerging cells. The values have been kept constant and a frequency reuse factor has been further considered. The results on the simulation provided an average of over 2000 understanding of the small scale as well as large value facings . Within the circular area and radium considered the user locations as well as a distribution a uniform basis within the cell. The value of shadowing and SNR has been found. The results have been analyzed and computed for the 200 user drops considered. For each of the sub-bands, a final simplified form of 40 has been retrieved. Based on this, these are averaged over the relative sub-bands as well as drops.
Apart from this, the author has considered the statistical analysis, single-user scenarios as well as multicellular cases with significant scenarios. In the cases, it has been evident that there significant match between the simulation outcomes as well as corresponding analytical results that are found to be on over large 40dB . Apart from this, it has been also observed that there is a loss of a certain extent within the throughput behind the differential feedback which is considered as a marginal with the increase in the number of antennas.
In the above pages of the report on wireless communication assignment, an accurate analysis has been done for throughput for different feedback based on the HLCS feedback scheme. It is considered for both the given standards that are 4G and 5G. This has been done for a different stream of single of a multi-antenna system for both single scenario and multi-user scenario within the co-channel interface. It has been already noticed that gains of subband fading were completely interrelated for differential feedback goods as CSI feedback. The analysis in the paper provides co-channel interference and different scheduler that covers a range of tradeoff between fairness and throughput. This highlight several insights like an increased throughput for correlation that exists between the sub-band which increases. Its focus on how differential feedback can help in reducing overhead to a significant amount.
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