Issues Of 4th Generation Computer Science Essay

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Fourth Generation (4G) is the upcoming technology using in cellular wireless standards. Today life styles of the people are become more critical and also much complicated. Therefore, wireless communication play a major role in the world helping people to communicated with each other fast and efficiently. 4G technology provides many services such as sending simultaneous use of voice, internet access gaming and streamlined multimedia services (TV and video streaming services).

In 4G, speed of communication and bandwidth are more reliable than early generation but there are disadvantages such as Multi-access interface, timing, inter cell interference, higher noise, security and higher cost of equipment. Problems arise due to frequency resources, short bandwidth, high required output power and limitation of coverage.[8] Ultra Wide Band (UWB) gives solutions for the problems of 4G. The characteristics of UWB short range, high data rate and low power radio technology. There are many advantages such as low complexity, low cost and have time domain resolution for location and tracking.

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In the real world main challenge of operating the over the multipath propagation channel, due to multiple reflections and co channel interference while propagating to the receiver through the channel path.[11] In this report further discussed the characteristics of UWB model channel and way of overcome the drawbacks of 4G.

In this project has designed UWB channel Simulink model between single OFDM transmitter and Receiver by using MATLAB Simulink. The channel model Simulink system optimized for interference and low power wireless network in range of 4G wireless system indoor environment applications. For this UWB channel model has designed by using MATLAB soft ware and has used IEEE 802.15.3a standard.

1.2 Aim and Objective

An Investigation of Ultra Wide Band (UWB) for 4th Generation wireless system. Mainly focus on drawbacks of 4G mobile communication which are interference and power parameters, find a solution by assess the suitability performance of Ultra Wide Band (UWB). It involves developing a communication system by designing UWB channel model in MATLAB simulation.

1.3 Objectives

Overview of UWB and 4G wireless systems

Design the appropriate UWB channel model diagram

Simulate the designed structure using MATLAB software

Performance of investigation and evaluate the best UWB range.

1.4 Report structure

Chapter 2- Describes the literature review of forth generation and Ultra wideband and characteristics of the technology.

Chapter 3 - Describes how the channel state information was

generated and what parameters were used in its generation.

Chapter 4- Describes the developed Simulink model and how

MATLAB was used to generate UWB channel system.

Chapter 5- Compares the results and analysis the performance of the UWB channel system with SNR and BER by observe the simulation curves.

Chapter 6- provides the conclusions of the project and the further developed.

Chapter 2- Literature Review

2.1 Fourth Generation (4G)

.

Fourth Generation stands for mobile communication that have many benifits . 4G provides a wide range of services such as higher data rate, high quality voice, and high quality video streams. The wireless approach of the technology will enable the users to access from anywhere. [10] 4G promising many features such as high speed, high capacity, Global mobility, service portability and Ad hoc networks and multi-hop networks. And another feature is its support interactive multimedia.

The 4G evolution UMTS standardized with Long Term Evolution (LTE) ,3rd Generation Partnership Project (3GPP)and WiMAX. Fast Fourier transform (FFT) technique has mainly consisted. Technologies for the antenna process have based on OFDM(orthogonal frequency division multiplexing) and MIMO (multiple-input multiple-output).

Property

4G

Starting Time

2010-2012

Driven Technique

Auto configuration

Representative Standard

OFDM, UWB

Radio Frequency (HZ)

3G-5G

Bandwidth (bps)

10M-20M

Multi-address Technique

FDMA, TDMA, CDMA

Cellular coverage

Mini areas

Core networks

All-IP networks

Service type

Multimedia ,Machine-to- Machine

Table 1 - 4th Generation Vision Summary [9]

2.1.1 Issues of 4th Generation

Interference - Higher frequency reuse leads to smaller cells that may cause intra-cell interference or higher noise figures due to reduced power levels.[8]

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Higher cost- Need for the digital to analogue conversions at high data rates, multiuser detection and estimation (at base stations), smart antennas and complex error control techniques as well dynamic routing will need higher cost equipment of sophisticated signal processing.

Delay- Voice over multi-hop networks is likely to be an interesting problem because of the strict delay requirements of voice.

Security

Quality of service (QOS) - QOS is vary and to have the network in better need a new IP protocol

Seamless roaming and seamless transfer of services.[8]

2.2 Ultra Wide Band (UWB)

Ultra Wideband based on the principle of radio technology. The Federal Communications Commission (FCC) and  European Telecommunications Standards Institute (ETSI) has standardised the UWB radio technology frequency spectrum range from 3.1 GHz to 10.6 GHz and transmit power of - 41.25 dBm/MHz. [9, ] UWB has the ability to transmit very high bandwidth over the short distance with low power efficiency and lower noise interference.

Fig-1 - Frequency Spectrum of UWB [11]

The Federal Communication Commision (FCC) defined the UWB to the broader category of signals, with including the fractional bandwidth should be greater than the 20% or bandwidth greater than 500MHz [6,7,12,20]. The relative bandwidth is defined by

Equation 2- Fractional Bandwidth of UWB[20]

Where FH and FL represent respectively the upper and lower cut off frequencies of the band defined at -3dB value . The high data rate is available only for the short distance due to the power limitations from FCC's on UWB transmission. Impulse UWB and multi carrier UWB are two basic types of UWB signals. In Impulse UWB (I-UWB) the transmitter transmits extremely short pulses to the receiver. I-UWB does not use a modulated sinusoidal carrier to convey information. Multi Carrier UWB (MC-UWB) uses many sub carriers to convey the information signal. This is a major characteristic of UWB because data can transmit without carrier wave that is UWB signal used as carrier frequency. [9, 12]

Parameter

Value

Bit Rate(Phy Layer)

110Mbps

200Mbps

480Mbps

Range

10m-30m

4m

2m

Power consumption

100mW

250mW

Target Error Bit Rate.

10-5

Table2 Summary of PHY Requirements[14]

2.2.1 Large Channel Capacity of UWB

The UWB will become ideal candidate for future radio communication systems in office , residential and ad hoc cause increasing of the data rate in wireless systems. Main charachteristic of the UWB is the width of the occupied frequency band. Typically it can be get 500MHz to GHz range values.

According to the Shannon's theorem, channel capacity C gives the reachable value of the theoretical maximum data rate in the channel. To transmit possibly the data rate with binary error rate (BER) lower than the fixed arbitrarily low threshold value. It means the data rate is lower than the theoretical value of the transmission channel capacity.[20]

Equation 1- Shannone Theorem Equation[20]

Where C- Channel capacity(bit/s), Bw- Signal bandwidth(Hz), S- Signal power level(W), N- Noise power level(W). According to the theory given bandwidth, the channel capacity increase in a logarithmic way with the values of the signal to noise ratio. But in this scenario the capacity increases linearly with the signal bandwidth while signal to noise ratio in constant .

To increase the demand of communication systems with high data rates, ratio technologies using a broad band spectral band are more capable to suggest convenient data rates to the applications. UWB frequency band reaching several GHz therefore well adapted to increase the data rate.[20]

2.2.2 Low power spectral density

The FCC has limited the power spectral density of UWB signals -41.3dBm.MHz-1 for the radio transmission. In other hand its advantage of low power spectral density which improved the safty of UWB radio communication by It more difficult to detect the transmission signals. The propagation distance is another consequence of characteristic. Therefore, as a result limit to 10 meters distance.[20] Hence applications of UWB systems are in short range and high frequency range.

UWB communications systems have an inherent immunity to detection and intercept because of their small average transmission power. Due to that the eavesdropper has to be very close to the transmitter around 1 meter to be capable to detect the transmitted information [22].

2.2.3 Less sensitivity to jamming

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UWB systems has occurred high processing gain therefore UWB signals relatively resistant to intentional and unintentional jamming of other signals. Out of frequency range some of frequencies can be jammed but large range of frequency remains with unharmed. Therefore Interference caused narrowband systems , performance depending on its modulation scheme and also UWB system is priori minimized by the bandwidth covered by the impulse signals [20,22].

2.2.3 High Performance in Multipath Channels

The large bandwidth can occurs from impulse signals transmitted waveforms. Normally narrowband suffer from fading related to the multipath which combines in a damaging way. The multipath presents delays lower than one nanosecond can be added in a useful way.[20] The effect of multipath signal has degraded up to -40 dB due to the out-of-phase addition of LOS and NLOS continuous waveforms. Advantage of UWB which short duration pulses have made less sensitivity of multipath effects. The next chapter will discussed the mechanism of multipath propagation.

2.2.4 Protected and Secured communications

UWB signals are high frequency range. Inherent characteristic of UWB signals difficult to detect. Hence spread over a broad band and transmitted with a low power spectral density and that is very closed to the noise floor level of traditional radio communication receivers. The UWB signal is noise-like therefore unintended detection quite difficult. Due to that these characteristics UWB enable secured transmissions communication with protection systems.[20]

2.2.5. Good obstacle penetration properties

The capability of penetration is advanced in UWB signals to go through in the walls and the obstacles. Mainly have ability for the low frequencies part of the spectrum. Therefore UWB signals have used in precision in terms of localization and tracking purpose.

2.3 Multipath propagation

Multipath signal occurs when transmitted signal take different paths to reach the destination. These path undergo various paths because of the surrounding objects. Due to that at the receiver occurs multipath delay, each of the presenting different attenuations and different phase rotation. Multipath propagation has three propagation mechanisms. which are reflection, diffraction and scattering.

Refection - Reflection occurs when an electromagnetic signal encounters a surface which is large compared to the wavelength of the signal. Eg surface of the building, walls etc.

Diffraction - Diffraction occurs incoming signal hits surface at the edge which has between transmitter and receiver of an impenetrable body. The edge is large compared to wavelength of radio wave.

Scattering - Scattering occurs when incoming signal hits an object whose size is smaller compared to the wavelength of the signal.

Figure 2.1-Mechanism of Multipath propagation

2.4 Fading in wireless communication

In wireless communication fading has occurred due to effect of multipath propagation. Multiple copies of signal may arrive at different phases to the receiver. There are two types of criteria to measure channel fading which are Doppler spread and Delay spread.

2.4.1 Doppler spread

The Doppler effect an observed shift in the frequency of an electromagnetic signal because of the variation of its propagation path. The transmitter is moving away from a receiver, the frequency of the received signal is lower than which sent out from the transmitter therefore cause Doppler effect. When considering the mobile receiver moving at a speed v and receiving a radio signal as a plane wave arriving with respect to the mobile direction with an angle α [20].The observed Doppler shift given by below equation.

Equation 2.2; Equation of Doppler Shift[20]

Where f is the signal frequency and C is the wave of propagation speed. The maximum Doppler shift is given at the Vmax.

In wireless communication there are many factors that can cause Doppler effect. Mainly relative movement of some background objectives which cause the change of path length between the transmitter and the receiver in the mobile radio environment. The length of signal path often could be different which correspond to different movement speeds of transmitter signals. And also has caused different frequency dispersion on the signal paths to the doppler effect.[12]

Small-scale Fading

(Based on Doppler Spread)

1.High Doppler Spread

2. Doppler spread of channel > Signal Bandwidth(channel variations faster than base band signal variation)

1.Low Doppler Spread

2.Doppler spread of channel < Signal Bandwidth( Channel variation slower than base band signal variation)

Slow fading and Fast fading cause due to the time dispersion wich is related to the Doppler shift effect. At the slow fading, base band signal varies faster than the coherence time, the distortion is negligible from the Doppler spread effect. The other situation of fast fading occurs when the baseband signal varies more slowly than the coherence time. Therefore that distortion is significant from Doppler spread fading effect.

2.4.2. Delay spread

Small scale fading

(Based on multipath time delay spread)

Flat Fading

BW of signal < BW of channel

Delay spread < Symbol period

Frequency selecting fading

BW of signal > BW of channel

Delay spread > Symbol period

When receiver have received multiple copies of signal with different moments from the transmitter which transmitted identical signal pulses. The signals reached to the transmitter in longer paths well as shorter paths. Which un-simultaneously arrival of signals occurred spread of the original signal in time domain. This is called delay spread.[23]

The frequency selectivity delay corresponds between signal propagation along different paths. In indoor environments this delay is in the order of a few nanoseconds. For the particular UWB signals presenting a very wide frequency band and time domain resolution is high, when limit the possible the interference between various delayed versions of the transmitted signals [20].