Spectral and Energy Efficiency in Device-to-Device Communications
The exploration of spectral and energy efficiency in device-to-device communications is crucial for optimizing performance in cellular networks. The discussion covers various scenarios, resource allocation methods, interference management, and network models, emphasizing the importance of considering factors like interference, location of terminals, and propagation channel effects to enhance network capacity and overall performance.
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Presentation Transcript
Spectral Efficiency and Energy Efficiency in Spectral Efficiency and Energy Efficiency in Device Device- -to to- -device Communications device Communications Paulo Cardieri Wireless Technology Laboratory - WissTek School of Electrical and Computer Engineering University of Campinas Second Workshop 5thGeneration of Mobile Networks October 17th, 2017 Inatel Santa Rita do Sapuca MG
Summary Summary Basic ideas A multitude of scenarios Performance metrics Simple model some results Enhancing the models Next steps
Device Device- -to to- -device communications device communications Communication between two User Equipments (UEs) in a cellular network is allowed: Improved channel reuse in the cell: spectral efficiency Reduced transmit power: lower interference level Reduced traffic load: lower interference level Reduced traffic in the core network (information traffic between base stations in no longer needed)
Several possible scenarios Several possible scenarios Partial coverage, relay Same cell, partial coverage In coverage, same cell Out of coverage In coverage, different cells
More scenarios More scenarios Resource allocation: In-band: D2D UEs use the cellular band Out-of-band: D2D UEs use other bands (e.g., ISM) Spectrum sharing: In-band overlay: D2D and cellular UEs use orthogonal resources In-band underlay: D2D and cellular UEs share the same radio resources Requires interference management UE link: Single hop vs. multihop
Network models Network models We are usually interested in analyzing the overall network capacity: Aggregate of transmission rate Average delay, etc. Interference is a key player in the network performance Models must include: Interaction among cellular and D2D terminals Location of terminals and base stations Propagation channel effects
Modeling location of terminals Modeling location of terminals Spatial Point Processes: describes in statistical manner possible patterns of node locations, within a given class. Instead of a detailed, particular description of node locations Poisson Point Process (PPP) Only one parameter: intensity (density of nodes) Nodes are randomly distributed in a 2D region Number of nodes per unit area: Poisson distributed Allows for closed-form expressions: Moment Generating Function of the aggregate interference
Spatial Point Processes Spatial Point Processes Point Processes usually employed in wireless network models Poisson Point Process Matern Point Process Poisson-Poisson cluster process
Performance Metrics Performance Metrics Some typical performance metrics Transmission capacity: Average data rate successfully transmitted per unit area ? = ? ? (1 ??) ? = link bit rate ??= Pr ???? ? Spatially averaged spectral efficiency ? = ? log 1 + ???? Local Delay
Simple model of D2D Simple model of D2D Cellular network Cellular network Two disjoint classes of user terminals: Cellular D2D One cellular terminal per cell Several D2D terminals per cell D2D terminals access channel with a given access probability p TX-RX separation distances are fixed (both cellular and D2D) D2D transmissions use uplink cellular channel
Simple model of D2D Simple model of D2D Cellular network Deterministic path loss ( ) and Rayleigh fading Cellular network: Base stations: Poisson Point Process, density ?? Cellular nodes: Poisson Point Process, density ?? ?? Active cellular terminals (one per cell): density ??= ?? TX-RX separation distance: ?? TX power: ?? D2D network: D2D nodes: Poisson Point Process, density ?? Effective density: p ?? TX-RX separation distance: ?? TX power: ?? Cellular network
Network model Network model D2D link ?? Base station Cellular terminal D2D terminal ?? Cellular link
Outage probabilities Outage probabilities Cellular terminals: 2? ?? ?? 2???? 2?? ??,?= Pr ??? < ?? = 1 exp 2???? + ?? D2D terminals: 2? ?? ?? 2??? 2?? ??,?= ?? ??? < ?? = 1 exp 2???? + ??? ??,??= SIR thresholds for cellular and D2D links
Spectral efficiency and Energy efficiency Spectral efficiency and Energy efficiency D2D Spectral Efficiency: ??= ?? log21 + ?? (1 ??,?) D2D Energy Efficiency ??=?? log 1 + ?? 1 ??,? ?? ??
Simple model of D2D Simple model of D2D Cellular network Cellular network We want to keep the performance of cellular links unaffected, as we attempt to increase the spectral efficiency of D2D links: Node density (or access probability) and transmit power of D2D terminals must be appropriately controlled [1]: 2? ??? ?? 2???? 2?? ??,?= 1 exp 2???? + ?? = fixed Fixed ?2 ? = ? D2D power control: [1] Pimentel, H.B., Cardieri, P., Optimization of Transmission Capacity of Cognitive Radio Networks," submitted.
Spectral efficiency and Energy Efficiency Spectral efficiency and Energy Efficiency Spectral Efficiency -5 Energy Efficiency 3x 10 2 10 d = 10 dB d = 10 dB Spectral Efficiency of D2D links Energy Efficiency of D2D links 2.5 0 2 10 1.5 -2 1 10 0.5 -4 0 10 -3 -2 -1 0 -3 -2 -1 0 10 10 Access probability 10 10 10 10 Access probability 10 10
Enhancing the network model (1) Enhancing the network model (1) Mode of operation [2] Mode selection Potential D2D UE q ?? ? D2D mode: ??> ? Cellular mode: UE 1-q Cellular UE Receiver location: D2D receiver is randomly distributed around the D2D transmitter Cellular receiver is randomly distributed inside the serving cell [2] X. Lin, J. G. Andrews and A. Ghosh, "Spectrum Sharing for Device-to-Device Communication in Cellular Networks," in IEEE Transactions on Wireless Communications, vol. 13, no. 12, pp. 6727-6740, Dec. 2014.
Enhancing the network model (2) Enhancing the network model (2) Spatial point processes: Cellular transmitters: cellular UE + potential D2D in cellular mode PPP, with effective density ?? ?= 1 ? ??+ ? ?? Pr ??> ? Potential D2D UE in D2D mode: PPP, with effective density ?= ? ?? Pr ?? ? ??
Enhancing the network model (3) Enhancing the network model (3) Potential D2D UEs autonomously decide whether or not to operate on D2D mode, based on sensing the channel. Opportunistic access Reduced communication overhead D2D mode: channel must be idle in the spatial domain [3]: Spatial spectrum sensing Channel is available if no active cellular UE is located inside the region surrounding that potential D2E UE. [3] H. Chen; L. Liu; T. Novlan; J. Matyjas; B. L. Ng; C. Zhang, "Spatial Spectrum Sensing based Device-to-Device (D2D) Cellular Networks," in IEEE Transactions on Wireless Communications , vol.PP, no.99, pp.1-1
Enhancing the network model (4) Enhancing the network model (4) ??= sensing range ?? Base station Cellular terminal Active D2D terminal Inactive D2D terminal D2D link Cellular link
Resulting Spatial Point Processes Resulting Spatial Point Processes Thinning process Thinning process is location- dependent Resulting point process is a Poisson Hole Process (no longer a Poisson Point Process) Difficult to analyze Investigation on good approximations is needed. Cellular UE Active D2D UE Cellular UE Potential D2D UE in D2D mode [3] H. Chen; L. Liu; T. Novlan; J. Matyjas; B. L. Ng; C. Zhang, "Spatial Spectrum Sensing based Device-to- Device (D2D) Cellular Networks," in IEEE Transactions on Wireless Communications , vol.PP, no.99, pp.1-1
Next Steps Next Steps Formulate performance metrics under this more general network model Energy efficiency, spectral efficiency Delay: imperfect spectrum sensing causes mutual interference between D2D UE and cellular UE - Coupled queues
