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52 Freeman (2004) states that there are a number of generic impairments that will directly or indirectly affect Quality of Service of voice, data, images etc. in telecommunication transmission systems. The following forms basic impairments in telecommunication networks and they include: Signal-to-Noise Ratio, Voice Transmission Rating, Amplitude (or attenuation) distortion and Phase distortion

Signal-to-Noise Ratio: Signal-to-noise ratio (S/N or SNR) is the most widely used parameter

for measurement of signal quality in the field of transmission. Signal-to-noise ratio expressed in decibels which indicate the amount by which signal level exceeds the noise level in a specified bandwidth. The types of material to be transmitted on a network each will require minimum S/N to satisfy the user or to make a receiving instrument function within certain specified criteria.

The following are S/N guidelines at the corresponding receiving devices (Freeman, 2004):

i. Voice: 40 dB;

ii. Video (TV): 45 dB;

iii. Data: ∼15 dB based upon the modulation type and specified error performance.

53 that will receive it), or round-trip, the way latency from source to destination plus the one-way latency from the destination back to the source (Vasseur et al., 2004). Latency is experienced when it takes a longer time than expected for each packet to reach its destination.

This is different from throughput, as the delay can build up over time, even if the throughput is almost normal. In some cases, excessive latency can render an application such as VoIP or online gaming unusable and directly affects the performance of network throughput.

Throughput: This is the amount of data which a network or entity sends or receives the amount of data processed in one determined time space. It has basic units of measurement, the bit per second (bit/s or bps). Due to varying load from other users sharing the same network resources, the bit rate (the maximum throughput) that can be provided to a certain data stream may be too low for real time multimedia services if all data streams get the same scheduling priority (Vasseur et al.,2004).

Jitter: Jitter is the delay variation and is introduced by the variable transmission delay of the packets over the networks. This can occur because of router’s internal queues behaviour in certain circumstances such as flow congestion and routing changes. This parameter can seriously affect the quality of streaming audio and/or video. To handle jitter, it is needed to collect packets and hold them long enough until the slowest packets arrive in time, rearranging them to be played in the correct sequences (Vasseur et al., 2004).

Packet loss: Packet loss occurs when one or more packets of data being transported across the internet or a computer network fail to reach their destination. Wireless and IP network cannot provide a guarantee that packets will be delivered at all, and will fail to deliver (drop) some packets if they arrive when their buffer is already full. This loss of packets can be caused by other factors like signal degradation, high loads on network links, packets that are corrupted being discarded or defected packets in network element (Vasseur et al., 2004).

54 Dropped packets: The routers might fail to deliver (drop) some packets if their data is corrupted or they arrive when their buffers are already full. The receiving application may ask for this information to be retransmitted, possibly causing severe delays in the overall transmission (Vasseur et al., 2004).

Errors: Sometimes packets are corrupted due to bit errors caused by noise and interference, especially in wireless communications and long copper wires. The receiver has to detect this and, just as if the packet was dropped, may ask for this information to be retransmitted (Vasseur et al., 2004).

Out-of-Order Delivery: When a collection of related packets is routed through a network, different packets may take different routes, each resulting in a different delay. The result is that the packets arrive in a different order than they were sent. This problem requires special additional protocols responsible for rearranging out-of-order packets to an isochronous state once they reach their destination. This is especially important for video and VoIP (Voice over Internet Protocol) streams where quality is dramatically affected by both latency and lack of sequence.

Figure 19: Overview of LTE Network Key Performance Indicator (Huawei Tech. Ltd. 2012).

55 Radio network KPI comprises elements that define the performances of the radio network while the Service KPI defines the elements focuses on users’ experience.

RRC SETUP SR: Radio Resource Control Connection setup Success Rate

ERAB Setup SR (VoIP, VoLTE/ALL): E-UTRAN Radio Access Bearer setup Success Rate.

(Voice over Internet Protocol, Voice over Long Term Evolution)

Call Setup SR (VoIP, VoLTE/ALL): Call Setup Success Rate Inter –RAT HHO SR: Inter Radio Access Technology Hard Handover Success Rate

Other Key Performance Indicators (KPIs) as employed by the SPECTRANET limited are as follows:

(i) Average Uplink (UL) and Downlink (DL) Throughput (Mbps)

(ii) Average Physical Resource Block Utilization Rate Per Cell (Percentage) (iii) Average number of User

(iv) Reference Signal Received Power (RSRP) (v) Reference Signal Received Quality (RSRQ) (vi) Signal to Noise Ratio (SNR)

(vii) Intra-eNodeB Handover Success and Failure Rate (viii) Average Downlink Channel Quality Indicator (DL CQI) (ix) Average DL and UL Spectrum Efficiency

(x) Average DL and Uplink Traffic Volume per Cell (xi) Average Service Drop Rate

(xii) Average DL and UL Transmission Block Retransmission Rate

56 2.7 LTE Radio Resource Management (RRM)

The aim of Radio Resource Management (RRM) in wireless communication networks such as LTE is to share the available and often limited radio spectrum between users as efficiently as possible (Vesa, 2007). The efficiency in RRM refers to the use of capacity in the sense of maximizing the data traffic load with respect to satisfying the QoS requirements. To ensure an efficient use of radio resources, several techniques are used as part of RRM. The main RRM algorithms/technique in LTE includes Admission Control, Power Control and Interference Control, and Packet Scheduling. (Dinesh, 2016):

Admission control: The first Radio Resource Management mechanism that a user new

encounter is the admission control process, which decides whether the services of the new user can be supported in the current traffic situation. Care in the admittance process is necessary, since admittance of several users demanding services could result in unacceptable outage and dropping potential for the users already in the network. If overload in the system should occur anyway, use of connection removal algorithms is obligatory to remove as few users as possible to guarantee the desired QoS level to the others (Vesa, 2007)

Power Control and Interference Control (PCIC): Since 3GPP only defines signalling regarding these procedures, they can be vendor and operator dependent. To overcome the fundamental difficulties of radio wave propagation in the environment of cellular networks, PCIC can be employed for monitoring and controlling the network traffic. Vesa (2007) generalised radio resource management algorithm/techniques as three they include:

i. Transmission Power Control: power control in wireless communication refers to intelligent setting and balancing of the transmission powers in respect of the available radio resources in the system.

57 ii. Adaptive Beam Forming: Adaptive beamforming provides a way to do spatial filtering of the signals in multiple-antenna systems in order to amplify the desired waveforms in respect to the interfering signals.

iii. Transmission Rate Allocation: Transmission rate allocation controls communication speeds of all connections with variable transmission rates in the system

Packet scheduling: An efficient mechanism is necessary to take advantage of a cell’s capacity, ensuring high spectral efficiency while guaranteeing the defined QoS to the connected users.

LTE’s solution resides in the scheduling of resources for both downlink and uplink channels in an intelligent and weighted way. Its main goal is the allocation of Resource Blocks (RBs) and transmission powers for each sub-frame in such way that a determined set of performance metrics is optimized. For the instance maximum/minimum/average throughput, maximum/minimum/average delay, total/per-user spectral efficiency or outage probability.

According to Ralf and Karstan (2011) the most critical function in the Evolved Universal terrestrial Random Area Network (E-UTRAN) is the Packet scheduling which is a sub-function and major function of Radio Resource Management (RRM) system. This sub-function can only be efficient with adequate scheduling algorithm. Adequate in this context means that it has to be handling network resources based on peculiarities because network behaviours, environment, topologies, deployment, capacity, users etc. differ, hence the importance of understanding adequate scheduling algorithm to suit each network operator. Adequate Scheduling algorithm ensures provisioned radio resources are utilized efficiently and Quality of Service is maintained across board. Scheduler is a very crucial tool in wireless communication in order to support increasing demand on data services such as mobile Television (TV), web. 2.0 services, content streaming, online video games etc. Schedulers tend

58 to provide adequate priority and fairness to all UEs, thereby improving and enhancing the cell throughput performance.

In International Telecommunication Union Radio communication Sector (ITU-R), scheduling algorithm is proprietary to network operator. Major kinds of scheduling algorithm or technique employed in LTE are (1) Best Channel Quality Indicator, (2) Round Robin (RR), (3) Proportional Fair Scheduler and (4) Max-Rate Scheduler.

2.7.1 Scheduling Algorithm in 4G LTE

Best Channel Quality Indicator (CQI): This scheduling algorithm is used strategically to assign resource blocks (RB) to the user with the best radio link conditions. The resource blocks assigned by the Best CQI to the user will have the highest CQI on that RB. The Mobile Station or UE must feedback its Channel Quality Indication (CQI) to the eNodeB to perform the Best CQI. UEs scheduling proceeds after eNodeB must have assessed the terminals Channel Quality condition instantaneously. Basically in the downlink, the BS transmits reference signal (downlink pilot) to terminals. These reference signals are used by UEs for the calculation of the CQI. A higher CQI value means better channel condition and more resource blocks from the scheduler

Round Robin (RR): The scheduler developed with this technique provides resources cyclically to the users without considering channel conditions into account. It goes in cycles, first come, first served and on equal proportion. The simple nature and procedure of this technique gives the best fairness to all users. However, the technique would propose poor performance in it comes to cell throughput and cell edge throughput. Round Robin technique meets the fairness to all by providing an equal share of packet transmission time to each user.

In Round Robin (RR) scheduling the terminals are assigned resource blocks (RB) in turn thus;

59 one after another without considering CQI values or any form of channel conditions. This means that the terminals are equally scheduled. However, throughput performance degrades significantly as the algorithm does not rely on the reported instantaneous downlink SNR values when determining time and radio frequency to be assigned as well as the number of bits to be transmitted.

Proportional Fair Scheduler (PF): Main purpose of Proportional Fair algorithm is to balance between throughput and fairness among all the UEs. The technique tends to maximize total wired and wireless network throughput while at the same time providing resource to all users at least at minimal level of acceptable service. Proportional Fairness was designed to maintain best access data rate. The scheduler applies Proportional Fair (PF) scheduling by allocating more resources to a user with comparatively better channel quality. This is done by giving each data flow a scheduling priority that is inversely proportional to its anticipated resource consumption. Users are scheduled based on the value of R/r, where R is the maximum data rate corresponding to the channel quality, and r is the average data rate of the user. Based on the radio channel quality of an individual user, the PF scheduler provides the user with an average throughput proportional to its average channel quality. In most cases, this algorithm is used to ensure fairness among users while achieving a moderate cell capacity.

Max-Rate Scheduler: UEs with higher data rate gets priority and preferential treatment, hence having more resource blocks assigned to than others with low data rate of consumption.