D2D, V2V, V2I

D2D

Operator Controlled D2D Communication and Challenges:


Overview:

  • Different from traditional device-to-device communication technologies such as Bluetooth and WiFi-direct, the operator controls the communication process to provide better user experience and make profit accordingly
  • Up to now, D2D is not in 3GPP, because the D2D function was only envisioned as a tool to reduce the cost of local service provision, which is fractional according to the operators’ current market statistics. However it is changing for several new market trends:
    • Context-aware applications as value added services provided by Operator
    • Cell Phone of a owner can be the hub for consumer electronic devices to connect to their networks; D2D from these devices to Cell Phone
  • Disadvantages of traditional D2D technologies like Bluetooth and WiFi-direct (although they are free) compared to Operator controlled cellular network:
    • Require manual pairing
    • Interference is uncontrollable on the crowded 2.4GHz unlicensed band
    • Cannot guarantee Security and QoS unlike a cellular network
Operator Controlled D2D Modes:
Controls - access authentication, connection control, resource allocation and lawful interception.
  • Fully Controlled D2D Mode:
    • Full control including control plane functions, e.g., connection setup and maintenance, and data plane functions, e.g.,resource allocations
    • Share cellular licensed band
    • Dynamic resource allocation like for normal cellular or semi-static dedicated pool for all D2D connections
  • Loosely Controlled D2D Mode:
    • Perform access authentication
    • Communication after is over unlicensed band (Bluetooth etc.,) or dedicated carrier on licensed band
    • Charged per month and can disable D2D anytime
Use Cases and Business Models:
  • Peer-to-Peer:
    • Local Voice Service: Offload local voice traffic.. e.g., in same supermarket
    • Local Data Service: Friends content sharing, multi-player gaming, local multicasting (shops advertise), machine-to-machine (e.g., phone to tv share), context-aware application (e.g., "check-in" at venues earn awards)
    • Advantages of operator controlled D2D services ("pay-for-what"):
      • Pay for Identity - Loosely controlled D2D to link phone number for WiFi Identity to share between devices
      • Pay for QoS and Security - Fully controlled D2D for high QoS and/or Security
      • Pay for context information - that operator has a lot of to leverage to
  • Relay:
    • UE as Gateway to Sensor Networks:
      • Cell phone as gateway for Sensors (M2M devices) on home devices, cars, or on-body healthcare devices
      • Advantages of operator controlled D2D services ("pay-for-what"):
        • Pay for management - non-cellular devices managed in operator subscriber database and associated to owner's cellular device; manage profile of owner and device specific access policies; meter data for sensors behind phone/gateway
        • Pay for QoS and Security - Fully controlled D2D for high QoS and/or Security (for ex., sensors for life care or security)
    • UE cooperative Relay:
      • UE as relay of another's information - risky and extra power consumption just for relay; not incentive enough for users
      • Future studies on achieving transmit diversity, multi-antenna transmission and network coding etc., thru cooperation
Technical Considerations in RAN:
  • Spectrum:
    • Unlicensed band: 
      • Using loosely controlled D2D; however uncontrolled interference
    • FDD licensed band:
      • UE to add additional Rx/Tx chain; more cost
    • TDD licensed band:
      • No additional Rx/Tx chain; share resources or allocate dedicated carriers
    • Guard band between TDD and FDD:
      • Half-duplex FDD in guard band
      • Cost-efficient still controlled
  • Power Control, Resource Allocation and Interference Management:
    • Distributively determined by UEs themselves:
      • Dedicated resources assigned statically (loosely controlled) or semi-statically (fully controlled) so that no interference (e.g., FlashLinQ)
    • Centrally performed by eNodeB (fully controlled):
      • Dedicated resources or share with cellular users
      • Emphasis for optimal performance on
        • Resource Sharing Mode Selection - D2D communication or not for a user pair; dedicated or shared with cellular users
        • Resource Allocation
        • Power Control Algorithms
      • Centralized resource allocation approach is explained in above Figure (proposal):
        • Assumed UE1 and UE2 already established D2D connection and UE1 has data wait to be sent to UE2
        • Resource allocation for most part looks similar to LTE, except:
          • Channel status of UE1<->UE2 link by periodic or aperiodic CQI reports from them thru PUCCH (estimated from SRS transmitted between them) to eNodeB
          • Then eNodeB notifies the resource allocation to both thru PDCCH, coded with C-RNTI
            • Two separate PDCCHs with separate C-RNTI's (uplink grant to UE1 and downlink grant to UE2) or 
            • One PDCCH with C-RNTI of UE1 (here UE2 needs to know UE1's C-RNTI then, during D2D connection establishment); reduce signalling overhead but increase the blind decoding attempts for the UEs
          • Then UE1 transmits data to UE2 on allocated resources
            • since it is D2D link, there shall be no difference link uplink or downlink, so better to use PUSCH both sender and receiver; else (UE1 sends uplink) UE2 needs to estimate downlink channel by detecting CRS and UE1 doesn't transmit CRS (only eNodeB does it); need devices to have uplink reception ability also for this
          • Then UE2 sends ACK/NACK on PUCCH
            • Reserve specific resources for D2D PUCCH or
            • Dedicated carrier for D2D ACK/NACK different from cellular ACK/NACK
        • No core network resources needed for D2D traffic; however, need a way to identify Application data passing thru PDCP to lower layers as to be sent to another device and not to eNodeB
  • Peer discovery, Paging and Connection Establishment
    • This is done of course prior to resource allocation and data transmission
    • Peer Discovery:
      • Centralized approach:
        • MME or PGW determines it is better to setup D2D connection
        • Informs eNodeB to request measurements and decide on D2D communication
      • Distributed approach:
        • UE broadcasts it identity for peers to aware of its existance
        • Flexible, but operator cannot forbid illegal users listening on licensed band
    • Paging and Connection Establishment:
      • Fully controlled D2D:
        • Normal as LTE, but need to inform to each UE of peer's C-RNTI, SRS configuration, ciphering key etc.,
      • Loosely controlled D2D on licensed band:
        • Once operator allows D2D connection setup, then a direct D2D paging for connection setup without eNodeB
      • Loosely controlled D2D on unlicensed band:
        • After authentication, then use traditional D2D for data transmission
Conclusion:
The operators still face several challenges in providing such a D2D solution that can address the below two “contradicting” objectives simultaneously:
  • Provide better user experience and make profit accordingly, yet..
  • Low-cost to compete with traditional free D2D communications

References

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