The modern mobile communication

ABSTRACT:

In latterly, new waveforms for 5G have been explored in many customs. It is not so easy for the modern mobile communication to assist the requirement of future mobile traffic. So that to overcome this issue, contemplates for 5th generation mobile communication has been accomplished. A new waveforms such as UFMC (universal filtered multi carrier), FBMC (filtered bank multi carrier),F-OFDM(filtered orthogonal frequency division multiplexing) and W-OFDM(windowed-OFDM) to be considered as a very substantial candidates for 5G system. In this paper, we have examined the spectral properties of waveforms. As experimental results, it is proved that the effective utilization of spectrum for each waveforms.

I.INTRODUCTION

The IOT (internet of things) and MTC(machine type communication) will play an important role in the future. But 5G is not only to about MTC. A crucial model consideration for 5G should be the valuable support of small packet transmission; it will provide a many future applications. Conventional orthogonal frequency division multiplexing has high-power out-of-band (OOB). As a result, adjacent channel interference (ACI) occurs. In order to avoid ACI, OFDM uses a wide guard band.

When a number of mobile devices access a base station simultaneously as a result it reduce the spectral efficiency. In OFDM systems coordinated multi-point(CoMP)communication techniques have been introduced. One of the major issues in CoMP-OFDM systems is their susceptiblity to multiple carrier frequency offsets (CFOs) between terminals and base stations. Due to Doppler shift resulting from terminals mobility or by oscillator frequency mismatch between a transmitter and a receiver the frequency offset may occur.

Multiple CFOs in CoMP-OFDM systems ruin the orthogonality between OFDM subcarriers and bring inter carrier interference (ICI) at the receiver which leads to degradation in system performance immensely. To overcome this problem filter bank multicarrier technique was suggested. DFT-precoding method is used in conjunction with CPOFDM to enhance single-carrier FDMA for carrying down PAPR because the only important difficulty in multi carrier modulation is high peak to average power ratio.

DESIGN CONSIDERATION FOR VARIOUS WAVEFORMS

OFDM

Is a multicarrier modulation technique, has broadly accepted for 4G communication systems(LTE and Wi-Fi).It has many benefits such as:

1.endurance to channel delays

2. Single-tap equalization in frequency domain

3.effective implementation. OFDM has some of disadvantages:

1. spectral efficiency loss due to higher side lobes

2.The stringent synchronization requirements. New modulation techniques are being contemplated for 5G communication systems to overcome the above issues.

FBMC

FBMC provide a solution to conquer the known limitation of OFDM of spectral efficiency reduction and stringent synchronization.

Transmit end processing operation:

Step 1: The prototype filter is a filter which is used for the zero frequency carriers and it is the base for the other subcarrier filters.
Step 2:The filters are exemplified by the overlapping factor which is denoted by K .It is the number of multicarrier symbols that overlap in the time domain.
Step 3:The order of prototype filter can be chosen as (2*K-1) where K = 2, 3, or 4 .
Step 4: The implementation of current FBMC uses frequency spreading. It uses an N*K length IFFT with symbols overlapped with a delay of N/2, here N is the number of subcarriers.
Step 5: To attain full capacity, FBMC use offset quadrature amplitude modulation. The imaginary part is delayed by half the symbol duration so that the real and imaginary parts of a complex data symbol are not transmitted simultaneously.

Receive end processing operation:
Step 1: The processing steps includes matched filtering operation then it followed by OQAM separation to form the received data symbols.
Step 2: These are demapped to bits and the resultant bit error rate is obtained.
Step 3:In the presence of a channel, linear multi-tap equalizers may be used to diminish the effects of frequency-selective fading.

The advantages of UF-OFDM over FBMC are:

• With short burst lengths, it provide better waveform spectral efficiency in time- and band limited
• CP-OFDM can be reused in UF-OFDM, while FBMC needs a lot of modifications.
• Due to orthogonality in complex plane, UF-OFDM with QAM modulation delivers full MIMO and CoMP support, but FBMC suffers lack of this complex orthogonality.

In LTE system at channel bandwidth of 20 MHZ .It uses 100 resource blocks and each having 12 subcarriers. An individual subcarrier is spacing of about 15 KHz. It leads to a 10 percent loss because only 18 MHz of allocated spectrum is utilized. In addition to this cyclic prefix of 144/160 samples is used per OFDM symbol so it leads to another 7 percent efficiency loss. so overall possible spectral efficiency is about 17 percent. Universal filtered multi carrier modulation technique which is known as a new modulation technique provides efficient spectrum usage.

UFMC is described as a generalization of F-OFDM (filtered OFDM) and FBMC modulations. In F-OFDM,the entire band is filtered and each subcarriers are filtered in FBMC, while groups of subcarriers are filtered in UFMC.This process of grouping a subcarriers allows one to reduce the filter length as compared with FBMC. To retains the complex orthogonality, UFMC can still use QAM which works with existing MIMO schemes.

Transmit end processing operation:

Step 1: The entire band of subcarriers denoted by (N) is divided into sub bands (group of subcarriers).
Step 2: A fixed number of subcarriers is present in each sub-bands for transmission.
Step 3: An N-pt IFFT is operated to each sub band and embedding zeros for the unallocated carriers.
Step 4: A filter filters each sub band having length( L), and the each sub-bands responses are added together.
Step 5: The filtering process is done to reduce the out-of-band spectral emissions. Different filters per sub- band can be adapted; here the same filter is used for each sub-band.
Step 6: For each sub-band, to filter the IFFT output by a Chebyshev window with parameterized side lobe attenuation is applied.

Receive end processing operation:

The receive processing of UFMC which is like OFDM is FFT –based.
Step 1: For the FFT operation, the sub-band filtering broadens the time window of receiver to the next length as power-of-two .
Step 2: Every value of alternate frequency belongs to a subcarrier main lobe. For balancing the joint effect of the channel and the filtering of sub-band purpose, per-subcarrier equalization is used in a system

The asset of Sub band filtering is compressing the guards between sub bands and also shortening the filter length, which construct this scheme fascinating for short bursts. The feature of latter also makes it pleasing in comparison to FBMC, which endures from much longer filter length.

Transmit end processing operation:
Step 1: The sub-band Cyclic Prefix-OFDM signal is applied through the designed filter.
Step 2: As the filter’s pass band belongs to the bandwidth of a signal, only the few subcarriers which are close to the edge are affected in this process.
Step 3: A major consideration in the F-OFDM is that length of the filter can be allowed to outstrip the cyclic prefix length.

Receive end processing operation:

The received signal is applied into a matched filter which is followed by the normal CP-OFDM receiver. It takes the measure for both the ramp-up filtering and latency prior to the FFT operation.

W-OFDM

It is a improved version of Orthogonal Frequency Division Multiplexing (OFDM)system. In the W-OFDM system processing chain it does not use the filter but for each OFDM symbol it uses the extension and windowing method as a result it reduce OOB power of spectrum.

III. CONCLUSION
A new waveform approaches such as UFMC, FBMC, F-OFDM and W-OFDM. These waveforms aid as an provider for the multiple access in order to manipulate the large collection of traffic types. From the simulation results the new waveforms have lower side lobes than the OFDM it implies that the spectrum utilization is effective in these waveforms.

FBMC is in a right path but it is still not ideal when applying practical applications it will arise many issues. Using UFMC we are capable to collect the advantages of FBMC and remove its major drawbacks. Like FBMC, UFMC is more potent to multi-user interference, provide higher spectral efficiency, greater performance in case of coordinated multipoint transmission and is better suited to fragmented spectrum than OFDM. UFMC is able to deliver complex orthogonality by avoiding many traps and compared to FBMC it improves at short burst/low latency transmission scenarios.

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