A Lte Advanced Comp Technique Computer Science Essay

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Coordinated multipoint transmission and reception is a new scheme based on Multiple Input Multiple Output for interference reduction in the 4G LTE-advanced. By acquiring coMP, it will eventually coordinate and combine all signals from multiple antennas which could lead to increasing of data transmission rate and maintaining of the service quality and throughput on the LTE broadband networks. As a result, 4G LTE-advanced network users can experience best internet access service which guarantee in consistent performance and quality at any time.

Introduction

Long-term evolution, also known as LTE, proposed by NTT DoCoMo of Japan in 2004, is a standard for wireless data communications technology used by mobile phones and data terminals. It is developed by the 3rd Generation Partnership Project (3GPP) through its Release 8 document series, which was later frozen in December 2008 and this has been the basis for the 1st wave of LTE equipment. The standard features high downlink and uplink rates, and QoS provisions, supports multi-cast and broadcast streams, along with the ability to manage fast-moving mobiles. Other than that, it also supports scalable carrier bandwidths.

The work by 3GPP to define a 4G candidate radio interface technology started in Release 9 with the study phase for LTE-Advanced. LTE-Advanced is a mobile communication standard that was approved into International Telecommunications Union (ITU), IMT-Advanced and was finalized by 3GPP in March 2011. Basically its a major enchancement of the LTE standard, with goals of reaching and surpass the ITU requirements, equipped with backward compatibility. One of the important LTE Advanced benefits is the ability to take advantage of advanced topology networks.

LTE Coordinated Multipoint (CoMP) is a technology that is being developed for LTE Advanced. It uses a method of transmitting to or receiving from a user equipment using several base stations, which results in better data throughput. Basically, it turns the inter-cell interference into useful signal, especially at the cell borders where performance may be degraded. By coordinating transmission among multiple cells, interference from other cells can be reduced and the power of the desired signal can be increased.

There are 2 categories of CoMP: Joint Processing (JP), where the data is available at each cell in CoMP coorperating set, and Coordinated Scheduling/ Beamforming (CS/CB), where the data is available at the serving cell (from the point).

LTE Overview: The Evolved Universal Terrestrial

Access Network (E-UTRAN) is the access part of the Evolved Packet System (EPS)

Fig.1: Access Network(E-UTRAN)

4G LTE CoMP:

- A single UE connected by multiple base stations.

- Simultaneous transmissioin

- Dynamic cell selection

Fig.2: Concept of LTE Advanced CoMP - Coordinated Multipoint.

* Fig.1 is retrieved from source [2]

* Fig.2 is retrieved from http://www.radio-electronics.com/info/cellulartelecomms/lte-long-term-evolution/4g-lte-advanced-comp-coordinated-multipoint.php

2.0 Technology and Technical Descriptions

2.1 The CoMP architecture

Coordination among eNBs is introduced to reduce inter-cell interference in the network in both the downlink and the uplink. CoMP is applied in the downlink by performing a coordinated transmission from the base station, whereas interference in the uplink can be reduced by means of a coordinated reception in eNBs. CoMP allows radio resources of different cells to be centralized and adaptively allocated to better handle the traffic fluctuations in each eNodeB, thereby achieving increased resource utilization across the entire network. [9] There are two kinds of architecture can be distinguished, which are centralized and distributed CoMP.

Centralized architecture

A central entity is needed to gather the channel information from all the UEs in the area which covered by the coordinating eNBs. This entity will then perform user scheduling and signal processing operation. Besides that, tight time synchronization among eNBs is needed and user data need to be available at all collaborating nodes. On the downlink of frequency division duplex (FDD) systems, the UE needs to estimate the channel and derive channel coherent or non-coherent indicators (CSI/CQI) to feed back to the eNB. The terminals must first estimate the channel related to the set of cooperating eNBs before the information is fed back to a single cell/anchor cell, which acts as the serving cell of the UE when coordination is being employed. Each eNB forwards it to the central entity that is in charge of deciding the scheduling and the transmission parameters. The new information will be sent back to the eNBs once the information is gathered. Fig. 1 has shown the centralized framework for coordination among different base stations.

Fig 3. Centralized CoMP architecture

Distributed architecture

Schedulers in all eNBs are identical and channel information regarding the whole coordinating set can be available to all cooperating nodes. Therefore, inter-eNB communication links are no longer necessary to perform cooperation. Thus, this architecture will minimize the infrastructure and signalling protocol cost associated with these links and the central processing unit which can prevent conventional systems from undergoing major changes. Moreover, the radio feedbacks to several nodes do not require additional overhead.

The procedure of distributed CoMP environment is UE will estimate the channel from all the coordinating eNBs in the very same way as in the centralized approach first. The estimates are then sent back to all cooperating eNBs and the scheduling is independently performed in each of them, as shown in Fig. 2. The same input parameters are expected to produce the same output decisions since the schedulers are identically designed, and therefore the same UEs are selected in the entire eNB cluster.

Fig. 4 Distribution CoMP architecture

*both diagram from Fig 3&4 are credited from [2] "The evolution to 4G cellular systems: LTE-Advanced"

2.2 Features of 4G LTE CoMP Coordinated Multipoint

LTE CoMP or Coordinated Multipoint is an underlying feature for LTE Advanced 4G Networks hat is still under current research and development. It is a still work in progress and with time the standards evolve. LTE Coordinated Multipoint is a series of different techniques that enable the dynamic coordination of transmission and reception over a variety of different base stations within an area.

The primary objective is to improve the overall service quality for the user as well as improving the utilization of the network. It takes advantage of the inter-cell interference and converts this into a useful signal especially at cell border areas where signal performance is known to be degradable. The basic features will be explored more in depth in the following chapter.

2.1.1 Primary features

The key advantages of LTE are high data rates which are achievable in LTE Advanced. These rates are easy maintained for users in close proximity to the base station but as the distance increases they become hard to maintain.

At the cell edges this is most difficult, due to the long distance from the base station it is affected by low signal strength putting into account that the interference levels from neighbouring base stations are likely to be higher as the end user will be closer to them. Coordinated Multipoint requires close coordination between a numbers of geographically separated base stations.

This way an end-user at the edge of the cell can be served by two or more base stations improving cell reception and increased throughput at the cell edge.

Fig 2.1 Interference of multiple signals at cell edge

4G LTE CoMP Coordinated Multipoint is broken down into major categories:

Joint processing: In this scheme the end user enjoys the benefit between multiple base stations that are both transmitting or receiving with the end user.

Coordinated scheduling or beam forming: This often referred to as CS/CB a setup of where end user is transmitting with a single transmission or base station. All this communication is made with an exchange of control among the different entities in the mobile communication network.

Highly detailed feedback is a requirement on the channel properties and should be done quickly.

The techniques for uplink and downlink are different due to the different relationships that exist between base stations that are connected in a network and between handsets that act as individual elements in the network.

2.1.1.1 Downlink LTE CoMP

The two formats for the coordinated multipoint can be defined for the downlink.

Joint processing schemes: The data is transmitted simultaneously to the end user from multiple base stations with an aim to increase the signal strength and also actively cancel other interference from other transmissions.

This places a huge load on the backbone of the network due to the amount of data sent to the each base station that is communicating with the end user. This is dependent on how many base stations are communicating with the end-user leading to signal delay and overheads.

Coordinated scheduling/Beamforming: In this situation a single end user is communicating with a serving cell like a normal non-CoMP transmission but the scheduling is dynamically coordinated between the cells. This way the interference from other cells can be minimized and controlled. In principle, schedule optimization will be performed based on the serving set of users, so that the transmitter beams are constructed to reduce interference to other neighbouring user, while increasing the served users' signal strength.

This method is favoured because of the reduction in the overhead on the backbone network due to the fact that end user data does not need to be transmitted across multiple base stations and only directed to one base station. Only the scheduling decisions and details of beams need to be coordinated across multiple base stations.

2.1.1.2 Uplink LTE CoMP

Joint reception and processing: It utilizes antennas that are geographically separated and through coordination a virtual antenna array is formed the signals received by the base stations are then combined to produce the final output signal. This allows for signal with low strength or interference to be received with few errors.

The main drawback is the amount of big overhead of data that is transmitted between different base stations.

Coordinated scheduling: This is to minimize interference the scheduling decisions between the base stations is coordinated.

Also with downlink this reduces the overhead on the backbone network because only scheduling data needs to be transferred between the different base stations that are coordinating with each other.

The end-user is not aware of the multi-cell reception of its signal, so that impact on radio interface specification is at minimal. Implementation of Uplink CoMP largely depends on scheduler and receiver in the cells.

One of the key features for LTE should be the ability to provide low latency levels. Now with the additional processing required for multiple site reception and transmission it could hinder that key feature. This will be due to the increase in processing times as well the overhead communications between different base stations.

2.3 Advantages and Disadvantages

2.3.1 Advantages:

Able to take advantage of advanced topology networks - optimized heterogeneous networks with a mix of macro-cells with low usage nodes such as pico-cells and femto-cells.

Improved capacity and coverage, and ensures user fairness.

Multicarrier ability - able to use ultra wide bandwidth, up to 100MHz of spectrum supporting very high data rates.

Comparing with predecessor LTE technology

Using the CoMP technique, many connections to several stations at once enables data to be passed through least leaded base stations, thus improving resource utilisation.

Better reception and increased received power as many cell sites can be used, therefore reducing number of dropped calls.

Multi-cell coordination significantly improves cell-edge user throughput.

Smooth access of high speed Internet whether they are in cell centre or at the cell edge.

Significant amount of exchange of information is possible since this communication is within a site.

Utilisation of the interference constructively to avoid the bad effects of interference.

Release 8 LTE

Release 10 LTE-Advanced

Capacity

200 active users in 1 cell (5Mhz)

3 times higher than LTE

Peak data rate

Downlink → 300 Mbps

Uplink → 75 Mbps

Downlink → 1 Gbps

Uplink → 500 Mbps

Peak Spectrum Efficiency

Downlink → 15 bps/Hz

Uplink → 3.75 bps/Hz

Downlink → 30 bps/Hz

Uplink → 15 bps/Hz

Scalable Bandwidth Support

Up to 20 MHz

Up to 20 MHz, with band aggregation up to 100 MHz

Table 1: The table above has shown the comparison of LTE version R8 and R10.

2.3.2 Disadvantages:

Due to the propagation loss, UEs who are close to the cell-edge also suffered from the degradation in the quality of the received signal.

As distance increase, maintenance becomes more difficult.

CoMP techniques require a highly detailed feedback on the channel properties constantly, increasing the amount of data needed to be transferred between the base stations for it to operate.

Requires very close coordination between the base stations to monitor the data flow or cell switching.

2.4 Comparison between the successor and predecessor of networks cellular systems

The first generation of the wireless telephone technology or mobile telecommunication networks were based on analog telecommunications standards. It was later being replaced by the digital technology known as the digital telecommunications which means that the main difference between 2G and 1G is that the radio signals that the 1G networks used were analog signals, whereas the digital signals are used in the 2G networks, the 1G speeds are between 28kbit/s and 56bit/s, which means the actual download speed may vary between 2.9KB/s to 5.6KB/s, AMPS family such as TIA/EIAIS-3 and other standards were use in the first generation cellular Network

While the second generation networks used digital signals there was some benefits over their predecessors were that the phone conversations were digitally encrypted, 2G system was significantly more efficient on the spectrum, the data services such as SMS text messages were first introduced by the 2G technology which also means higher speeds than 1G technology. (GSM/3GPP family, AMPS family and other standards were involved in 2G cellular network technology. Moreover, both technologies have used digital signalling to connect the telephone system to the radio towers.

The third generation of wireless mobile communication systems also known as 3G, improved spectral efficiency over 2G and 2.5G technologies and addresses the demand for higher bit-rates, which means it provides an information transfer rate of at least 200KB/s . The third generation networks do not use the same radio frequencies as the second generation's, so mobile operators must built new networks with new frequencies for the third generation networks in order to be used.

Then comes the fourth generation "also known as Beyond 3G" of the wireless communications, and the first release of Long Term Evolution(LET-advanced),however it has been debated whether the first versions of this technology should be considered to be 4G or not. LET-Advanced also make use of additional spectrums and multiplexing in order to allow it to achieve higher data speeds, by using fully IP-based system the expected data rates to be in the range of 100-1000Mbit/s. Coordinated Multi point Transmission also allow more system capacity to help handle the enhanced data speeds as well.

LET-Advanced data speeds for peak download approximately 1Gbit/s, as for uploaded data 500Mbit/s.

In comparing to the 3G technology, more specifically in terms of end usage is that the data transfer speeds provided. This means the users are able to access much more sophisticate data which requires a lot of bandwidth very quickly. Of course depending on the service provider, however, 4G technology could be limited to specific zones for making calls which are generally smaller than covered by 3G technology, which means one who is trying to make calls would have his/her call dropped once they are outside the covered area.

3.0 Discussion

Development of LTE-Advanced in Malaysia

In Malaysia, Maxis Sdn. Bhd is the first Telco Company to offer 4G LTE service which rides on the 1800MHz & 2600MHz spectrums. Maxis 4G LTE claims that the speed is up to 75Mbps and typical average speeds of 10Mbps to 30mbps*. [2] However, the coverage of Maxis 4G LTE is now only available in certain areas of Selangor state from 10 April 2013 onwards. [3]

The coverage of LTE networks will be increased in due time as the charge of LTE-Advanced service will decrease when the 4G LTE-Advanced getting popular.

Drawbacks and challenges of the CoMP

The main challenge for centralized CoMP architecture is related to the new associated communication links between the central entity and the eNBs. A very-low latency data transmissions and in addition communication protocols for this information exchange are needed.

The distribution CoMP architecture presents some drawbacks. The performance of the CoMP algorithms is less efficient if different eNBs do not perform cooperation via a wired backhaul. Besides that, the handling of errors on the different feedback links is another concerning problem. The same UE reports its channel conditions to all the eNBs in the set but the wireless links to the different nodes might be very different. Hence, the impact of these errors on the system performance cannot be neglected.

Even though there are some drawbacks of CoMP, but i strongly believe that there will be a good research to eliminate and increase the efficiency of the LTE-Advanced network in due time.

Besides that, it has been claimed by a research studies that the signal power will be degraded if coordinating on more cells. Coordinating more cells may translate into less interference from other cells, but also weaker signal power for the end-user and heavier overhead messaging burden. [11]. Hence, at current stage, researchers may need to think for better algorithms in order to reduce the impacts of coordinating on signal power.

4.0 Recommendation

In order to improve CoMP, we must deal with the challenges.

The complexity of DL CoMP can be managed in real-world scenarios and that significant gain can be realized by forming small cooperation clusters in large-scale networks. However, solutions for the following are needed before it can be integrated in next-generation mobile networks:

Reduced cost of base station synchronization and low-phase-noise transmitters

Efficient feedback compression

Reduced feedback delay

Efficient channel prediction at the precoder

Flexible formation of cooperation clusters

Handling of outer interference within the cluster

Efficient multi-user selection

Flexible networking behind CoMP

Integration of CoMP into higher layers [8]

In order to enhance the CoMP, both of the hardware and software must be optimized. At the hardware part, fibre optics cable should be acquired to connect inter and intra base station. The fiber optics cable has the fastest transmission rate and less susceptible to the noise and signal degradation. It is no use that the transmission speed in wireless is fast but drag by the slow copper wires at base station at last. Fiber connections among distributed cooperating points and regrouping the scheduling and processing functions at a central BBU allow harnessing the highest CoMP gains. Deployment of CoMP in the network pertains to the propagation environment and the expected traffic load. [10] To ensure the quality of network, the number of 4G LTE users should be limited at start before the network is fully utilized. This is because the immature development of LTE-Advanced network probably may not afford the huge number of users. Besides that, the high charged imposed at start will create profitable revenue for the company.

Conclusion

CoMP is a very promising technique which could really enhance experience of current LTE-Advanced. By acquiring CoMP technique, the interference problem of on edge cell will be reduced.

In my opinion, a huge investment on evolution of 3G network to 4G LTE-Advanced is a must for now. This is because the growth of global internet connection demands has grown exponentially. The demand of internet will never decrease because when the number internet connection will be increasing until internet is available to everyone. However, there will a demand of faster downlink and uplink speed and better quality of service even if there is no growing space for number of internet user.

It is no doubt that internet will become irreplaceable and essential in the coming future as the demands of internet connection has getting bigger and bigger. Therefore, ISP should really concern of the demands of the market and provide a better network in term of system and quality of service. In short term view, the development of latest networking technology will create new revenues for company. However, it will eventually realize cost saving for the company in long term as the technology has become mature and the equipment become cheaper by day.

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