Mobile Communication And Significant Technical Differences Computer Science Essay

Published: Last Edited:

This essay has been submitted by a student. This is not an example of the work written by our professional essay writers.

The Fourth Generation (4G) technology candidates is foreseen most likely to be between Long Term Evolution Advanced (LTE-Advanced) proposed by the Third Generation Partnership Project (3GPP) and Mobile WiMAX using 802.16m standardised by the Institute of Electrical and Electronics Engineers (IEEE). Distinguish the technical differences between these two technologies and give your opinion on the scenario and deployment of 4G in the near future.

Significant Technical Differences

1. LTE and WiMaX employ the orthogonal frequency division multiple access (OFDMA) in the downlink. But WiMax optimizes for highest channel handling by developing all the information in a wide channel. LTE, in contrast, arranges the available spectrum into smaller portions. WiMax pays a charge for high channel utilization, however, because developing that much information might involve a 1,000-point fast Fourier transform. LTE can obtain by with a 16-point FFT. This interprets into higher power consumption, because it's complicated to design fixed-function WiMax hardware that is also resourceful in LTE designs.

2. LTE applies single-carrier frequency division multiple access (SC-FDMA)[9] for uplink signaling, whilst WiMax sticks on OFDMA.

3. Even though both the IEEE 802.13e standard and the evolving LTE standard hold up frequency division duplexing(FDD) and time division duplexing(TDD), WiMax applications are principally TDD. LTE seems to be going in the FDD direction because it is right full-duplex operation: Adjacent channels are applied for uplink and downlink. LTE can therefore estimate a better spec for downlink data rates, though at a cost of placing very severe latency conditions for forward error correction. The main thing is that the WiMax radio is much uncomplicated.

At the end of 2007, the overall mobile users were 3 billion, with GSM based users to raise over 2 billion. Some research reports are expecting that the WiMAX will viably be implemented by 2009 and the LTE (Long Term Evolution) by 2015. Nevertheless, the standards conflict towards the 4G launch is a major concern. ITU and IEEE are attempting to secure a smooth conversion into the new technology. (Figure 1)

Figure 1: Smooth conversion into the new technology

There are various methods that can be used to increase user and system capacity such as by using new multiplexing scheme with enhanced modulation schemes. Tabulate and summarize some important features related to the multiplexing and modulation techniques for analog system (e.g. ETACS, AMPS) and digital (e.g. GSM, GPRS, EDGE, HSPA, LTE, WiMAX) system. Among them are FDMA, TDMA, CDMA, SDMA, etc. for multiplexing and FM, GMSK, 8-PSK, QPSK, OFDM, MIMO, Adaptive Modulation and Adaptive Modulation and Coding (AMC).





Frequency Division Multiple Access (FDMA)

Frequency Modulation(FM)


Frequency Division Multiple Access(FDMA)

Frequency Moduation(FM)



Time Division Multiple Access(TDMA)

Gaussian Minimum Shift Keying (GMSK)


Time Division Multiple Access(TDMA)

Gaussian minimum-shift keying (GMSK)


Time Division Multiple Access(TDMA)

8 Phase Shift Keying (8PSK)


Code Division Mutiple Access(CDMA)



Multiple Input Multiple Output (MIMO)

Orthogonal Frequency Division Multiple Access(OFDMA)



Orthogonal Frequency Division Multiple Access(OFDMA)

Table 1: Multiplexing and modulation technique for analog and digital system

The public cellular service operator in Malaysia are subjected to mandatory standards for Quality of Service (QoS) or Grade of Service (GOS) by Malaysian Communication and Multimedia Commission (MCMC). List various parameters and schemes used for providing QoS/GOS in cellular network and discuss their advantages/disadvantages to the subscribers and operators. How can QoS provisioning be managed in the future 4G cellular network?

There are difference schemes of QoS in cellular netwoks:

1.0 Fault Tolerant Dynamic Channel Allocation Scheme [1]

In this scheme the channels are assigned dynamically based on requirement and therefore increase the channel utilization as well as the quality of service (QoS). The channel allocation schemes are unified and distributed. In a unified approach, the central controller is in charge for channel allocation and it will send a request to the controller whereas in distributed approach, a channel allocation in particular cell is handled by Mobile Service Station (MSS). Therefore, algorithm is used in this approach.

Figure 1: A Model of Wireless Communication Networks [3]

Figure 1 shows a wireless communication model. Many cells consist Mobile Hosts (MH) and a Mobile Service Station (MSS)[3]. A Mobile Host will request a channel from MSS in order to communicate with another Mobile Host .In communication, there are communication channel and control channel [3]. A communication between a MH and a MSS is supported by communication channel while control channel is employed for transfer control messages in order to set a communication channel. The channels are assigned by MSS to the MH to see if there is co-channel interference occurs. A channel for communication is allocated to the MH if the co-channel interference does not exist.

There two different approaches for requiring channels. In Centralized approach, Mobile Switching Center (MSC) will be used to provide channels for each MH if MH asked for a channel from the central controller. Hence, the MSC will prepare for channel allocation in condition that no co-channel interference exists. In this approach, the MSC might become a bottleneck in the network [3] and the whole network will be affected if the MSC experiences break down. This is the drawbacks of the Centralized approach. Hence this approach is not scalable and robust [3].

In Distributed Approach, each cell has its own MSS and the central controller does not present. The neighbors of a cell will receive an update about channel utilization by the cell and notifies them when to quit the channel so that others can use it. A cell can use a channel right after getting a reply from its entire neighbors informing the cell that the channel is ready to be used.

1.1 System Model [3]

Channels are assigned dynamically and not assigned in advance to any cells. A cluster model is employed where three cells are used with each cell has six neighbors. If a cell uses a channel, its neighbor cannot use the same channel in order to avoid co-channel interference. If the cell does not have any channel, it can borrow a channel with a condition that the cell's neighbors satisfied its request and also ensure that co-channel interference does not exist. There are two types of operation mode which are update mode and search mode [3]. A notification of a cell about its channel utilization information to all its neighbors is known as update mode. A cell is able to send an update about its status to its entire neighbors by using this mode. In addition, a cell can send a request message to its neighbor if it wants to borrow a channel and this type of operation is called search mode.

1.2 Distributed Channel Allocation Algorithm [3]

In this model, there are three cell cluster model with each cell in a cluster has six neighbors which a unique neighbor ID is assigned from one to six to the cells. A channel is not pre-assigned for the cells.

Figure 2: Distributed Channel Allocation illustrated by Cell Cluster Model [3]

In figure 2 each cell is indicated by number one to six and we are going to use cell i to indicate a particular cell. The cell i is in search mode when this cell request for a channel to use (this cell is called 'borrower'. The cell is sending broadcast message to all its neighbor requires for a channel and setting a timer. Once it got replies from its neighbor, cell i will borrow a channel and the timer will times out after the cell got a channel. A cell will ignores any query from any other cell when it is in borrower mode. This type of scheme is good in the way that it avoids unnecessary congestion in the network[3].

2.0 Call Admission Control (CAC) Scheme[3]

Call Admission Control Scheme control call arrival by estimating its rates continuously. When the new arrival call is higher than predetermined level, hence some calls will be blocked. Pre-request scheme and the Guard Channel scheme are used to compare new arrival call rates and the pre-determined level. In the Guard Channel Scheme several channels are exclusively stored for the handoff calls. While in the channel pre-request scheme the channels are ask in advance before the handoff occurs. There are various benefits and drawbacks which are given by these two schemes. However, the development of CAC algorithm offers a better QoS compared to the two schemes. The Forced Termination Probability (FTP) is used in CAC algorithm. FTP is used to indicate the ratio of calls which are forced to terminate when the calls fail to handoff.

3.0 QoS based on Mobility Prediction Techniques[3]

Mobile prediction techniques are used to search for the path of a mobile node and it is stored in a database from time to time. This technique assists in reserving resources for Mobile Host before a handoff take places so preference resources take over a node before its handoff and therefore this reduces the call blocking rate at handoffs. On the other hand, the new call contact rate is diminished as more resources are stored for handoff calls. FTP can be decreased by adding the number of new call blocking possibility. But this is not very resourceful deployment of the radio resources. By using Mobile Prediction Methods, we can predict earlier when a handoff will take place and so dynamic distribution of resources for the handoff can be done. These will make sure that the upcoming call blocking probability is not increased so much to keep resources for the handoff calls. There are numerous mobile prediction techniques which have been utilized in the past which includes GPS positioning techniques.

4.0 Dynamic Allocation Scheme using Renegotiation [3]

In a Dynamic Allocation scheme using Renegotiation, the unemployed resources of the network are searched and they are allocated to services which got a smaller bandwidth at the time of access when they actually asked more. In other words, renegotiation of the bandwidth is prepared for a lesser priority service when the medium is free, thus rising the entire bandwidth of the lesser priority services. This scheme also conversely keeps the bandwidth of the higher preference sources.


The Very Small Aperture Terminal, VSAT service is becoming more popular in Malaysia. Obtain information on VSAT service operator in Malaysia including examples of application, network topology, user equipments, lease procedure and services offered and their data rate. How can a VSAT system accommodate subscriber that need higher data rate services.

VSAT Applications

VSAT is an ideal satellite network that offers communications support for a wide range of applications [7]:

Point-of-sales transaction[7]

Order-Entry Billing[7]

Inventory Control[7]

Financial Management[7]

Data processing[7]

Reservation System[7]

Telemetry & Data Collection[7]

News Wire Services[7]

Private-Line Voice[7]

Virtual Private Networks[7]

Distance Education[7]

High Speed Internet Access[7]

VSAT Topology

The VSAT system has two types of topologies: Star Topology and Mesh Topology

1.0 Star Topology

The star topology is the conventional VSAT network topology. The remote terminal is connected to the hub for communication. It suitable to used this topology for data collection or broadcasting. The hub station (double hop) is used to communicate between the remote and this makes star topology impractical to offer speech services between the terminals because time delay in the hub station (500 ms) is high. The digital carriers provide connection on the space segment in both directions, which organized with a variety of access schemes. The access techniques used in a star network can be Frequency Division Multiple Access (FDMA)[9], Time Division Multiple Access (TDMA)[9], and Code Division Multiple Access (CDMA), but TDMA is the most common.

2.0 Mesh Topology

In mesh topology, there is direct communication between the remote VSAT terminals. This direct communication reduces the time delay. The signaling processor is placed in the central node, hence this internal signaling is using star topology and this is often referred to as the demand assignment multiple access (DAMA). While in a mesh network, it is typically for Frequency Division Multiple Access (FDMA).

Figure 1: VSAT system topologies: star topology and mesh topology. Mesh topology offers direct connectivity between the remote VSAT terminals [6]

End User Equipment for satellite Internet access[7]

The end user equipment consists of the VSAT dish, BUC LNB and the Modem which depending on where to place the equipment and they are classified as indoor or outdoor.

1.0 The indoor unit[7]

The IDU is normally a single box satellite Internet modem which is linked to the customer's computer equipment.

1.1 Satellite Modem

A Satellite Modem is used to set up data transfers by employing a communications satellite as a relay [7]. The VSAT Systems Indoor Unit (IDU) modem has involved TCP optimization and Quality of Service (QoS) potential, router and DNS. The unit is centrally controlled from a Network Operations Center (NOC) [7].

The IDU is well-matched with Ku and C band service as well as Ka band service when IDU becomes available [7].

2.0 The outdoor unit[7]

2.1 VSAT Satellite dish

The satellite dish which is in parabolic shape is mounted on the roof. From the geostationary satellite, the dish will receive signals and transfer the received signal to the modem. The dish sizes vary between 0.96m to 2.8m [7].

VSAT networks in common function at one of three frequencies: C band, Ku band, or Ka band. C band operation requires a huge satellite dish due to its lower frequency. However it suffers less from rain attenuation. Ku band dishes are lesser in size and more susceptible to rain-fade than C band dishes. On the other hand, Ku band dishes work well even during rain fade situations if the modems are put with power boosting capabilities. Ka-band-based network is able to employ even smaller dish sizes, but, the difficulty of rain attenuation is exaggerated further at the higher frequency operations such as Ka [7].

Larger dishes supply for better response in remote areas and maintain much higher bandwidth service plans. The dishes can be stationary, mobile or portable[7].

2.2 Block up Converter[7]

The uplink of satellite signals is using Block Up Converter (BUC) that works by exchanging a 'block' (band) of frequencies from a lower frequency to a higher frequency. As the distances to be traveled by the signal for transmission are tremendous, higher frequencies are employed as they suffer less attenuation. BUCs switch the L band to a Ku band and a C band to a Ka band[7].

For most applications, BUCs have a rating between 3-6 Watts. BUCs with larger ratings are offered for other high powered applications [7].

2.3 Low Noise Block Converters (LNB) [7]

BUCs are normally used in conjunction with Low Noise Block Converters (LNB)[7]. The BUCs make up the 'transmitting' section of the equipment whereas LNBs are down-converters, the receive section of the equipment. Ku band signals received from the satellite are high frequency signal that suffer greater attenuation while passing through cable. Therefore the receive signal requires to be down converted in order to reduce attenuations.

VSAT Services [8]

i. Interactive real time application[8]:

- Point of Sale/retail/Banking (eg. ATM) [8]

- Corporate data[8]

ii. Telephony[8]

- Rural: individual subscribers[8]

- Corporate Telephony[8]

iii. Intranet, Internet and IP infrastructure[8]

- Multimedia delivery (eg. video streaming) [8]

- Interactive distance learning/ training[8]

iv. Direct-to-home[8]

Broadband Internet access for consumers and businesses[8]

VSAT data rates

The list of data rates (in Kbps) is as below;

  1. 1.2 up to 56

    6. 512

  2. 64

    7. 768

  3. 128

    8. 1024

  4. 256

    9. 1536

  5. 384

  10. 2048

How can a VSAT system accommodate subscriber that need higher data rate services.

VSAT networks give a way to set up a switched point to point data network that can have the capability for high data rates of up to 2Mb/s. Connections are set up directly between remote terminals usually on a call by call basis. These networks are generally configured to operate without a large central earth station and carry a mix of data traffic and telephony traffic or only data traffic.

Direct Broadcasting Satellite, DBS service such as ASTRO is becoming more popular. Investigate and research the multiplexing method each TV channels before the channels can be distributed and shown to viewer. How can ASTRO solve the problem of signal impairment and degradation due to heavy rain, and interference from WiMAX operators?

In digital television and radio system, a fixed bit-rate data streams is generated by multiplexing some variables of bit-rate data streams by means of statistical multiplexing. Hence, video and audio channel can be transferred simultaneously over the same channel along with a variety of services.

There are several Standard Definition Television (SDTV) programme (mostly on DVB-T, DVB-S2, ISDB and ATSC-C), or one HDTV. The device that achieves this is called a statistical multiplexer. The newer DVB standards DVB-S2 and DVB-T2 have the ability to carry several HDTV channels in one multiplex [6]. If the most advanced MPEG-4 compressions hardware is used,the original DVB standards can carry more HDTV channels in a multiplex [6].

On communications satellites which carry broadcast television and radio network which is called Multiple Channels per Carrier or MCPC [6].If multiplexing is not realistic, single channel per carrier mode is employed [6].

Signal multiplexing of satellite TV and radio channels is usually carried out in a middle signal playout and uplink centre, such as Astro in Malaysia, which offers playout, digital archiving, multiplexing for some of digital TV and radio channels [6].

How can ASTRO solve the problem of signal impairment and degradation due to heavy rain, and interference from WiMAX operators

The direct-to-home (DTH), is broadcast as high-power Ku-band transmissions using the transponders of the MEASAT satellite system. Reception of the service signals utilizes a fixed 60-cm diameter dish antenna.

Ku-band signals can be influenced by rain attenuation (rain fade), making it vulnerable to frequent outages in heavy rainfall areas such as Malaysia, the operators of Astro have utilized a tailor-made system to increase power of the satellite delivery system to overcome this problem. The service availability of 99.7%, however, is still a issue of much debate by subscribers.