5G Communication Technology 5G technology is currently being considered for use in 28 and 36 GHz bands. These frequency bands are referred to as the millimeter band (mm-band). Consequently, 5G communication is often termed as millimeter-wave communication. 5G technical requirements compared to 4G

5G Technical Challenges Ultra fast data transmission (Gbps data rates) 5G will provide ultra fast data transmissions (Up to 50 Gbps), by combining several innovative solutions like, mmWave technology, massive MIMO, advanced modulation and coding approaches, etc. 2) Superior user QoS: Uniform Gbps data rates and superior user QoS throughout the whole cell, by introducing solutions like, massive MIMO aided beamforming and small cells. Smaller network latencies will be provided by utilizing advanced solutions like software defined networking.

5G Technical Challenges 3) Massive multiple access It is expected that 5G will provide up to 100 times higher number of simultaneously connected devices, compared to legacy systems. Solutions like, massive MIMO aided interference alignment, D2D communication, and Cloud RAN 4) Cost effectiveness 5G systems are envisioned to provide up to 50 times more cost effective operation Solutions like small cells, network function virtualization, multi-RAN interworking, etc.

5G technical solutions 1) mmWave Communications Small transmission range of mm-wave band leads to smaller coverage area (Smaller cell radius). So, the use of directional antenna becomes a necessity. High penetration loss and signal absorption. Smaller cell radius and signal absorption effectively mitigates the inter-cell interference and provides better cell coverage

2) Massive MIMO and Beamforming Massive MIMO, provides several advantages as, significantly improved spectral efficiency, improved channel response and simplified transceiver designs. Massive MIMO significantly reduces channel estimation errors due to uncorrelated noise and interference . mmWave facilitates massive MIMO with practical and small scale designs (e.g. up to 256 antenna elements on an area of 8 cm2) By introducing 2D planar arrays and further exploiting the elevation dimension, the so-called full-dimension MIMO (FD-MIMO), i.e. 3D-MIMO, can incorporate higher number of antennas within the same form factor

Massive MIMO and Beamforming The forthcoming research activities will focus on finding the optimal tradeoff between the power gain required for efficient mmWave operation and the interference tolerance margin required for optimal spatial multiplexing performance, in order to attain the maximal system capacity. Table 2 show that the combination of mmWave and massive MIMO provides drastic increase of system capacity.

3) Device-to-Device (D2D) communication Device-to-Device (D2D) communication allows two UEs to exchange information on direct D2D links, bypassing the eNB. Network that supports D2D communication has two kinds of Ues: D2D UEs (DUEs) Conventional cellular UEs (CUEs)

Connection setup between two DUEs in D2D communication While eNB does not act as a relay for the participating DUEs, it plays an active role in setting up their connection. After a D2D connection is established eNB is taken out of the picture.

Modes of Operation Overlay mode Underlay mode Network that supports D2D communication can operate in either the underlay or overlay modes Overlay mode Assigning different frequencies to CUEs and DUEs Wastes bandwidth CUEs have to tolerate a certain decrease in their data rates. CUEs and DUEs do not interfere with each other Underlay mode Both DUEs and CUEs operate on the same frequency band. Better frequency reuse and spectral efficiency Lead to considerable interference between CUEs and DUEs that are reusing the same frequency.

D2D Communication Underlaying LTE-A the transmit power and resource allocation for CUEs and DUEs must be carefully handled In order to underlay D2D communication Transmit Power Control The transmit power of DUEs has not been standardized yet. eNB should select the transmit power of DUEs based on the power levels currently used by the CUEs Assign different priority levels to CUEs and DUEs while controlling their transmit power. In order to ensure that priority is given to CUEs, their SINR level is monitored continuously. If the SINR of CUE drops below a specified threshold, the transmit power of DUE reusing the same resource has to be reduced.

D2D Communication Underlaying LTE-A Resource Allocation In underlaying D2D communication, a CUE and a D2D pair reuse the frequency that causes minimum interference. Interference Tracing (IT) scheme: The eNB broadcasts the Radio Resource Management (RRM) messages that contain the information on uplink resource allocation DUEs determine the CUEs which are expected to cause interference that is lower than a specified threshold. Tolerable Interference Broadcasting (TIB) scheme: The eNB estimates and broadcasts the tolerable interference for each radio resource. DUEs select only those resources that cause smaller interference to eNB than the advertised value.

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