4th Generation (4G)

4G is the name given to the fourth generation of mobile phone mobile communication technology standards. It is a successor of the third generation (3G) standards.It provides mobile ultra-broadband Internet access.

SWITCHING BETWEEN MODULATION SCHEMES

if the performance of the modulation schemes as the figure, Switching between modulation schemes is done to maintain a BER less than a certain BER the next figure as the desired BER less than 10^-3.

CHARACTERISTICS OF WIRELESS CHANNEL

The wireless radio channel poses a severe challenge as a medium for reliable high-speed communication. It is not only susceptible to noise, interference, and other channel impediments, but these impediments change over time in unpredictable ways due to user movement.

Adaptive or Fixed Modulation

This experiment to made to know which is the better adaptive modulation or fixed modulation The experiment is applicable to both TDD and FDD systems,provided that accurate predictions of the channel conditions exist.For each prediction of the SNR at the receiver, the modulation scheme is selected for 512 consecutive symbols.

Diversity

The diversity is a technique that combating the fading by ensuring that there will be many copies of the transmitted signal which effected with different fading over time, frequency or space.

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4th Generation


4th generation

4G


4G or LTE is one of the most growing technologies used in communication  systems to enhance the services of mobile communications  or use better service
  
4G is the name given to the fourth generation of mobile phone mobile communication  technology standards. It is a successor of the third generation (3G) standards.It provides mobile ultra-broadband Internet access.

4G is around five times faster than existing 3G services. Theoretically it can provide download speeds of up to 100Mbps and 50Mbps for upload. This makes 4G is more than twice as fast as the latest 3G technology and many more times faster than previous versions. but these speeds are theoretical, and we won't achieve this in real-world use.

However, that doesn't mean 4G isn't twice as quick. In our tests, which we'll get to later, we saw speeds around three times faster on 4G compared to 3G, and an even larger improvement with uploads.

The faster speeds mean websites load quicker, and that you'll be able to stream videos and podcasts without first waiting for them to buffer. Plus, you'll be able to download large email attachments or other content from the web faster. Apps which need to download data, such as maps, will work more smoothly, especially when zooming in or out as this generally requires a lot of data. The speed differential should be akin to switching from 3G to Wi-Fi.

For video streaming and similar tasks, where you would typically require Wi-Fi for smooth performance, 4G should allow you to have a 'home broadband' experience on the move. EE expects the average speed to be between 8- and 12Mbps, potentially faster than the 5.9Mbps average for ADSL home broadband.

Faster upload speeds will also be a boon. If you hate waiting for pictures to be posted to Facebook or Twitter, for example, then this should be a much faster process over 4G.
  
4G networks use different frequencies to transmit data than 3G so we need a handset which has a modem that supports these new frequencies.

Two forms of 4G been developed and are in use: WiMAX and LTE.

In fact, we may recognize the first technology, as WiMAX was trialled in the UK in 2009. However, the first WiMAX network was launched by South Korean firm KT in 2006.

'LTE'  Stands for Long Term Evolution and is a type of 4G technology
The first LTE network was deployed in Scandinavia in 2009. However, it was debatable whether the speeds on offer back then were really 4G or not.
4G LTE aims to offer users faster, more reliable mobile broadband internet for devices like 
devices like smart phones,tablets and laptops. 

4G technology:

The main reason 4G is faster than 3G is because of Orthogonal Frequency-Division Multiplexing (OFDM). It sounds complicated, but it's the same technology used in Wi-Fi, ADSL broadband, digital TV and radio.

OFDM is a technique for squeezing more data onto the same amount of radio frequency. It also reduces latency and interference. Data is split up and sent via small chunks of frequency in parallel, therefore increasing the capacity of the network.

Multiple-input and multiple-output, or MIMO, is another reason 4G is able to provide faster speeds. It is simply the use of multiple antenna arrays at both the transmitter and receiver to improve communication performance.

This allows more data to be transferred without requiring additional bandwidth or drawing more power. The most common configuration currently is a 2x2 MIMO, found in many smart phones and some tablets. A 4x4 setup is also possible and promises even faster speeds but is still a little way off making its way onto devices. Since different setups are possible, one phone could provide faster 4G speeds than another.
With 3G handsets, most of us take roaming for granted. We take our phones travelling around the world, and expect to be able to pick up emails and browse websites as soon as we land. Things are different with 4G.
Although there are 4G networks in many countries around the world, your UK 4G Smartphone won't necessarily work wherever you go. The reason is that 4G doesn't operate on the same frequencies in every country.
 

 4G frequency bands: 

Technology
 Frequency  spectrum
3G
850MHz
    900MHz
1900MHz
2100MHz
4G
800MHz
    1800MHz
2600MHz

Wi-Fi
2400MHz
     5000MHz


Bluetooth
2400MHz



 

4G coverage:

EE says it will provide 4G coverage in a total of 10 UK cities at launch, with 16 switched on by Christmas. The firm says it means 20 million users will be able to get the faster speeds before the year is over. The lucky cities to get 4G before the rest of the country are:

Birmingham, Bristol, Cardiff, Edinburgh, Glasgow, Leeds, Liverpool, London, Manchester and Sheffield.

4G improvements

than 3G:

   



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intro to GSM

intro to GSM
GSM 

 Before talking about the GSM system and the features and the bands in details of this system i will talk quickly about  the 1G and the 2G(GSM) standard using some pictures and little words.

Single Cell Systems :

 

The single cell system suffers from handover (the call is disconnected when moving from one cell to the other ) as shown in the figure 
 
and the solution of this problem is  to use the cellular systems

Cellular Systems:

 


1st & 2nd Generations:

   

  2nd Generation Standards:



  


GSM Phases:



Why Wireless

Why Wireless
Wireless 
 

Why Wireless?


All of us use at least one wireless device and most of us ask a question to himself why wireless!!!! 
in this simple article i will try to answer this question 

firstly i will discuss The kinds of transmission medium to know why the wireless is better in some words 

1- Twisted-pair:

 It is very low bandwidth and it is easily tapped either physically or by monitoring its electromagnetic radiation

2- Coaxial cable:

It is greater bandwidth than twisted-pair but it is very expensive.

3- optical fibers:

It is very high bandwidth , very high bit rate.

4- Radio (wireless):

It is greatly depending on the particular frequency of the electromagnetic wave

Some of Radio advantages

a- They are very flexible and suitable for all terrain
b- Portable system can be installed very quickly
c- There are often the most cost-effective solution

 

Two-Ray Model

Two-Ray Model
Ray Tracing (2)

Wireless Channel Problems 


The two-ray model is used when a single ground reflection dominates the multipath effect, as illustrated in the next figure 
The received signal consists of two components: 
The LOS  component or ray, which is just the transmitted signal propagating through free space, and a reflected component or ray, which is the transmitted signal reflected off the ground. 
 
The received LOS ray is given by the free-space propagation loss formula 

The reflected ray is shown in the previous figure by the segments x and x′
If we ignore the effect of surface wave attenuation then, by superposition, the received signal for the two-ray model is 
 
where τ = (x + x′ − l)/c is the time delay of the ground reflection relative to the LOS ray,root of (G1) = root of (Ga*Gb)  is the product of the transmit and receive antenna field radiation patterns in the LOS direction, R is the ground reflection coefficient, and root of (Gr) = root of (Gc*Gd)  is the product of the transmit and receive antenna field radiation patterns corresponding to the rays of length x and x′, respectively. The delay spread of the two-ray model equals the delay between the LOS ray and the reflected ray: (x + x′ − l)/c. If the transmitted signal is narrowband relative to the delay spread (τ << Bu) then u(t) ≈ u (t −τ). With this approximation, the received power of the two-ray model for narrow-band transmission is 
where Δφ = 2π( x + x′ − l)/λ is the phase difference between the 
two received signal components. the previous equation has been shown to agree very closely with empirical data . If d denotes the horizontal separation of the antennas, ht denotes the transmitter height, and hr denotes the receiver height, then using geometry we can show that  
 
When d is very large compared to (ht + hr) we can use a Taylor series approximation in the previous equation to get 
 
 The ground reflection coefficient is given by

 
We see from the first figure  and the last equation  that for asymptotically large d , x + x′≈ l ≈ d , θ ≈ 0 , Gl≈Gr , and R ≈ −1. Substituting these approximations into 

yields that, in this asymptotic limit, the received signal power is approximately 
 
or, in dB, we have
 
Thus, in the limit of asymptotically large d, the received power falls off
inversely with the fourth power of d and is independent of the wavelength λ. The received signal becomes independent of λ since combining the direct path and reflected signal is similar to the effect of an antenna array, and directional antennas have a received power that does not necessarily decrease with frequency. 
A plot of  the following equation  
as a function of distance is illustrated in this figure

for f = 900MHz, R= -1, ht= 50m, hr= 2m, Gl= 1, Gr= 1 and transmit power normalized so that the plot starts at 0 dBm. This plot can be separated into three segments. For small distances (d <ht) the two rays add constructively and the path loss is roughly flat. More precisely, it is proportional to 

since, at these small distances, the distance between the transmitter and receiver is

and thus 

for ht>>hr, which is typically the case.

For distances bigger than ht and up to a certain critical distance dc, the wave experiences constructive and destructive interference of the two rays,resulting in a wave pattern with a sequence of maxima and minima. These maxima and minima are also refered to as small-scale or multipath fading. At the critical distance dc the final maximum is reached, after which the signal power falls off proportionally to d^-4. This rapid falloff with distance is due to the fact that for d >dc the signal components only combine destructively, so they are out of phase by at least π. An approximation for dc can be obtained by setting Δφ = π in 

,obtaining dc = 4hr ht/λ, which is also shown in the figure. The power falloff with distance in the two-ray model can be approximated by averaging out its local maxima and minima. This results in a piecewise linear model with three segments, which is also shown in the next figure slightly offset from the actual power falloff curve for illustration purposes. In the first segment power falloff is constant and proportional to 

,for distances between ht and power falls off at -20 dB/decade, and at 
distances greater than dc power falls off at -40 dB/decade. The critical distance dc can be used for system design. For example, if propagation in a cellular system obeys the two-ray model then the critical distance would be a natural size for the cell radius, since the path loss associated with interference outside the cell would be much larger than path loss for desired signals inside the cell. However, setting the cell radius to dc could result in very large cells, as illustrated in the next figure and in the next example. Since smaller cells are more desirable, both to increase capacity and reduce transmit power, cell radii are typically much smaller than dc.
Thus, with a two-ray propagation model, power falloff within these 
relatively small cells goes as distance squared. Moreover, propagation in cellular systems rarely follows a two-ray model, since cancellation by reflected rays rarely occurs in all  directions. 


Ray Tracing

Ray Tracing(1)

Wireless Channel Problems



In a typical urban or indoor environment, a radio signal transmitted from 
a fixed source will encounter multiple objects in the environment that produce reflected, diffracted, or scattered copies of the transmitted signal, as shown in the next figure These additional copies of the transmitted signal, called multipath signal components, can be attenuated in power, delayed in time, and shifted in phase and/or frequency from the LOS signal path at the receiver. The multipath and transmitted signal are summed together at the receiver, which often produces distortion in the received signal relative to the transmitted signal.
 
In ray tracing we assume a finite number of reflectors with known location
and dielectric properties. The details of the multipath propagation can then be solved using Maxwell’s equations with appropriate boundary conditions. However, the computational complexity of this solution makes it impractical as a general modeling tool. Ray tracing techniques approximate the propagation of electromagnetic waves by representing the wave fronts as simple particles. Thus, the reflection, diffraction, and scattering effects on the wavefront are approximated using simple geometric equations instead of Maxwell’s more complex wave equations. The error of the ray tracing approximation is smallest when the receiver is many wavelengths from the nearest scatterer, and all the scatterers are large relative to a wavelength and fairly smooth. 
Comparison of the ray tracing method with empirical data shows it to accurately model received signal power in rural areas, along city streets where both the transmitter and receiver are close to the ground, or in indoor environments with appropriately adjusted diffraction coefficients. Propagation effects besides received power variations, such as the delay spread of the multipath, are not always well-captured with ray tracing techniques. If the transmitter, receiver, and reflectors are all immobile then the impact of the multiple received signal paths, and their delays relative to the LOS path, are fixed.
However, if the source or receiver are moving, then the characteristics of
the multiple paths vary with time. These time variations are deterministic when the number, location, and characteristics of the reflectors are known over time. Otherwise, statistical models must be used. Similarly, if the number of reflectors is very large or the reflector surfaces are not smooth then we must use statistical approximations to characterize the received signal.
Hybrid models, which combine ray tracing and statistical fading, can also 
be found in the literature, however we will not describe them here. The most general ray tracing model includes all attenuated, diffracted, and scattered multipath components. This model uses all of the geometrical and dielectric properties of the objects surrounding the transmitter and
receiver. 
Computer programs based on ray tracing such as Lucent’s Wireless
Systems Engineering software (WISE), Wireless Valley’s Site Planner_R, and Marconi’s Planet_R EV are widely used for system planning in both indoor and outdoor environments. In these programs computer graphics are combined with aerial photographs (outdoor channels) or architectural drawings (indoor channels) to obtain a 3D geometric picture of the environment