GFDM modulation forms for wireless communication
1. Introduction
FDM means dividing the entire frequency band into different smaller frequency bands to be used by different users. Different frequencies are combined into a composite signal and transmitted on a single link. Each signal can be treated as a channel. Some Frequency division Multiplexing techniques are:
1. OFDM - Orthogonal frequency-division multiplexing
2. OFDMA - Orthogonal frequency-division multiple access
3. GFDM - Generalized Frequency Division Multiplexing
4. SEFDM: Spectrally efficient frequency division multiplex, etc.
In this article, I will discuss the GFDM and GFDM modulation forms.
2. GFDM
GFDM stands for Generalized Frequency Division Multiplexing. Which is one of the best solutions for the 5G physical layer because it can address the different requirement. GFDM is a flexible multicarrier modulation scheme. The modulation is performed block by block, where each GFDM data block consists of a certain number of subcarriers and sub symbols. By setting the number of subcarriers and the number of sub symbols to 1, GFDM allows single-carrier frequency domain equalization (SC-FDE) and CP-OFDM as its special cases, respectively. Furthermore, pulse shaping with a prototype filter is another flexibility in GFDM to reduce out-of-band (OOB) emissions. In contrast to linear convolution used in FBMC, GFDM brings circular convolution into play.
In figure 1, GFDM is flexible multicarrier technology, which will introduce more degrees of freedom. The structure of modulated GFDM data is shown in the figure, with the GFDM symbol one CP [Circular Prefix] of the symbol.
In summary, GFDM can be derived:
1. Proposed for the physical later, 5G of wireless communication networks
2. Non-orthogonal waveform, circularly pulse shaped
3. GFDM is one of the noticeable non-CP-OFDM-based waveforms
4. Low out of band radiation to avoid harmful interference
5. Frequency and time domains multi-user scheduling
6. Block based transmission using cyclic prefix insertion
3. GFDM Modulator
The block diagram of the considered GFDM transmission scheme is shown in Fig. 1. In this scheme, the transmitter part includes several blocks. By using a matrix notation, the vector of input bits b is applied at the input of the encoder. The encoder splits the high bit-rate stream into a number of lower bit-rate streams and forms the encoded vector bc. The vector bc is applied at the input of the mapper which gives at its output an N × 1 data vector d whose elements take values from a complex constellation, e.g., QAM. The data vector d is then applied at the input of the GFDM modulator that contains N elements. The block diagram of the GFDM modulator matrix is given in the Fig. 3. The data vector d can be decomposed into K groups of M symbols according to
d= [(d0)^T, (d1)^T…… (dk-1)^T]^T
with
dk = [dk,0,dk,1,.....,dk,M-1]T ,
where dk,m corresponds to the QAM symbol transmitted on the k-th sub-carrier and in the M-th sub-symbol of the block and (?)T denotes transposition. The time-duration of each data block dk is MTs and the sub-carrier spacing is equal to 1/MTs.
4. Properties of GFDM
There are four properties that can be described as GFDM properties, which are
1. Multi-carrier scheme
2. Block based approach
3. Circular Signal Structure
4. Overlapping sub-carries
4.1 Multi-carrier scheme: Multi-carrier modulation is dividing the data stream transmits to a number of lower data rate streams. Every lower data rate stream is then used to modulate the individual carriers. In GFDM multicarrier modulation schemes used closed spaced non-orthogonal carrier and provide flexible pulse shaping.
4.2 Block based approach: GFDM is a block filtered multicarrier system which is generalized the concept of OFDM, including numerous circularly pulse-shaped sub symbols per subcarrier. Each and every block consist of a certain number of subcarriers and sub symbols. The block structure comprising of N=KM tests where K subcarriers constitute a GFDM sub-symbol and M GFDM sub-symbols constitute a GFDM symbol.
5. GFDM Modulation Techniques
There are several techniques I have read in different articles, among of them there are two popular and effective modulation techniques I have found which are:
1. IM (Index Modulation)
2. Multiple Input and Multiple Output (MIMO) – GFDM
5.1 IM (Index Modulation of GFDM)
Index modulation (IM) refers to a family of modulation procedures that depend on the activation states of a few resources/building blocks for data inserting. The resources/building blocks can be either physical or antenna, subcarrier, virtual parallel channels, space-time framework, and antenna activation arrange. A particular include of IM is that portion of the data is certainly inserted into the transmitted signal. The IM concept over classical OFDM, such as adaptable framework plan with a flexible number of active subcarriers, moved forward blunder execution for low-to-mid spectral efficiencies, and basic handset plan, we accept that tight integration of GFDM with the IM concept incorporates a solid potential to fulfill the predicted prerequisites of future remote systems in a satisfactory way. In expansion, the combination of the IM strategy with GFDM has been investigated where a throughput loss was gotten due to the unused subcarriers.
5.2 Multiple Input and Multiple Output (MIMO) – GFDM
MIMO (multiple inputs, multiple yields) is an antenna technology for wireless communications in which multiple antennas are utilized at both the source (transmitter) and the destination (receiver). The antennas at each end of the communications circuit are combined to minimize errors and optimize data speed. MIMO-GFDM plans are given through the proposed system and their bit error ratio performances, computational complexities, and spectral efficiencies are analyzed. It has been illustrated that the inter-symbol interference and noise will be diminished with better performance.
6. GFDM For 5G
5G wireless technology is implied to provide higher multi-Gbps peak data speeds, ultra-low latency, more reliability, gigantic network capacity, expanded accessibility, and a more uniform user experience to more users. Higher performance and improved efficiency enable modern user experiences and connect new industries. In OFDM there is some severe problem to achieve the 5G capabilities because of high latency and lower spectrum efficiency, GFDM overcomes these issue in multiple ways and it is always open to adapt new technologies like MIMO or Index modulation so GFDM is more capable to provide the 5G features as well as researchers thinking GFDM modulation with 6G technology also.
7. GFDM comparison to OFDM
1. In OFDM, each symbol requires a cyclic prefix (CP), which depends on the tap length of the channel. The addition of CP diminishes the spectral proficiency and anticipates getting a low latency by shortening the symbols. In OFDM Compared with GFDM technology, GFDM utilizes fewer cyclic prefixes and, as a result, incorporates a higher spectral efficiency.
2. In GFDM, the concept is precisely the same as OFDM but the symbols are shaped by Gaussian beat forming. It has way better transmission capacity effectiveness and way better co-channel interference.
3. In Performance comparison GFDM has better PAPR, BER, and OOB than OFDM.
8. Advantages
1. In GFDM, the OOB(Out of Band) emission is significantly low and it can serve for divided and artful spectrum assignment purposes. GFDM uses a single CP for a whole block that contains numerous subsymbols. This empowers frequency space equalization (FDE) and progresses the spectral efficiency.
- Higher robustness against carrier frequency offset (CFO)
- Higher robustness against sampling time offset
4. The block structure of GFDM can be designed according to the requirements, especially for systems with limited bandwidth
9. Conclusion
GFDM is a novel solution for the 5G physical later because its flexibility can address the different requirements. It combines both advantages of specific subcarrier allocation and low PAPR. Low PAPR allows reducing the hardware cost and power consumptions, which is an important point for wireless systems.
10. References:
1. Wu, J., & Kang, P. Emerging 5G Multicarrier Chaotic Sequence Spread Spectrum Technology for Underwater Acoustic Communication. Hindawi.
3. Ivan S Gaspar, Luciano L Mendes, Nicola Michailow & Gerhard Fettweis: A synchronization technique for generalized frequency division multiplexing. EURASIP Journal on Advances in Signal Processing,2014
4. https://link.springer.com/referenceworkentry/10.1007%2F978-3-319-32903-1_143-1
5. Ersin ?ztürk, Ertugrul Basar, Ertugrul Basar, Hakan Ali Cirpan: Generalized Frequency Division Multiplexing With Flexible Index Modulation, IEEE, October 2017
6. Shwetal K. Antapurkar, Avinash Pandey, and K.K.Gupta : GFDM Performance in terms of BER, PAPR and OOB and comparison to OFDM system, AIP Conference Proceedings, October 2015