2. Related Work
- We propose an algorithm to activate the optimal number of LWA UEs, accounting for the accommodating capacity of the WLAN network, as well as guaranteeing QoS for LWA UEs.
- We prove with numerical results that our proposed algorithm achieves better system throughput gain, compared with a random mechanism and an LTE-W mechanism.
- The complexity of our proposed algorithm holds to only O(QM2) for worst-case time complexity, whereas eNB can hold Q APs, comprised of M UEs, and MlogM is the complexity in sorting.
- We present a detailed procedure for LWA activation and deactivation.
3. System Model
3.1. Problem Formulation
3.2. Challenges on an Unlicensed Band
3.3. The Proposed LWA Algorithm
|Algorithm 1. The proposed algorithm for optimum allocation of LWA UEs.|
3.4. LWA Activation and Deactivation Procedures
3.4.1. For LWA Activation
- The RRM entity of the eNB gets the packet data convergence protocol (PDCP) layer to configure the bearer of the UEs to the WLAN. Configurations of bearers can be of two types: a switch or a split bearer.
- Switch bearer: Since only one data path is possible, the RRM suggests PDCP for switching the bearer configuration from LTE to WLAN only.
- Split bearer: The LB entity commands execution of split scheduling at the PDCP layer that strips the incoming packets (PDCP protocol data units [PDUs]) of the LWA UE bearer into two links. However, the data transmission ratio between the links can be variable based on the traffic condition and load of the WLAN network, which is outside the scope of this article.
- Before a PDU is transmitted by the WLAN interfaces, the LWA adaptation protocol (LWAAP) entity processes the data and generates an LWAAP PDU containing a DRB identity (DRBID) (a one-byte header to each PDCP PDU). Furthermore, Ether Type 0X9E65 is added by the WLAN AP for forwarding LWA data packets to UEs over the WLAN. Later on, this information is used by UEs to identify the LWA bearer of the receiving PDU.
- After reception of data by UEs, the UEs differentiate the LWA packets from normal packets by processing them through the LWAAP entity, where the LWAAP header is removed, and then forwards the packets to the PDCP instance based on the DRBID. In return, an LWA status report is sent via LTE to the eNB to acknowledge correct reception of the LWA packets.
- The LWA status report constitutes the first missing sequence number (FMS), the highest received sequence number on the WLAN (HRW), and the number of missing PDUs (NMP).
- Based on LWA status feedback through UEs, the eNB maintains traffic through the WLAN for LWA UEs.
3.4.2. For LWA Deactivation
- The RRM entity of the eNB requires the PDCP layer to use the default bearer configuration, which is LTE for UEs.
- PDUs will be sent through an LTE-only path to UEs.
4. Numerical Results
Conflicts of Interest
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|Complete name||LTE in unlicensed/License Assisted Access||LTE WLAN Aggregation||LTE WLAN Integration with IP Tunneling||Multipath TCP|
|Leading work group (WG)||RAN WG1||RAN WG2||RAN WG2||MPTCP WG1|
|Release||Release 12/Release 13||Release 13||Release 13||RFC6824, etc.|
|Protocol layer||Link layer (MAC layer)||Link layer (PDCP)||IP layer (IP tunnel)||Network layer (MPTCP)|
|New device function||UE and eNB (5 GHz LTE)||PDCP||IPsec||MPTCP|
|Network element||LTE-U/LAA small cell||LWA eNB, WT||LWA eNBs, LWIP-SeGW||MPTCP Proxy|
|Traffic direction||Downlink||Downlink||Uplink + Downlink||Uplink + Downlink|
|Access network cost||High (new LTE small cell with LTE-U/LAA @ 5 GHz)||Medium (new small cell: LWA aware WLAN terminal)||None (uses existing WLAN AP)||None (uses existing WLAN AP)|
|BS and AP distance||50~100 m|
|Downlink bandwidth||20 MHz|
|Noise power||−174 dBm|
|Path loss for cellular links||15.3 + 37.6log10(d)m|
|Path loss for unlicensed band||15.3 + 50log10(d)m|
|Transmission power of eNB||36 dBm|
|Transmission power of AP||24 dBm|
|Number of WLAN UEs||2~10|
|Number of LTE UEs||20~40|
|WLAN bit rate||1 Gbps|
|PHY Header||192 bits|
|MAC Header||224 bits|
|Slot time||9 μs|
|ACK||112 bits + PHY header|
|RTS||160 bits + PHY header|
|CTS||112 bits + PHY header|
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