Licensed-Assisted Access

Licensed-Assisted Access:

LAA is intended to allow Wi-Fi and LTE-U to coexist through Clear Channel assessment (CCA)/ Listen Before talk (LBT) and Opportunistic use of spectrum which increases capacity. LAA is a part of 3GPP Release 13, it has been deployed in European countries and Asia. LAA supports Gigabit class LTE i.e. 5Gbps in near future. LAA Combines LTE in unlicensed 5GHz downlink with licensed LTE by Carrier Aggregation (CA) and aim for new small cell deployments. AT&T reported as saying LAA is better option than LTE-U as it has less cost of spectrum, uses the mechanism like LBT as seen it is a good technique to reduce interference and certified by 3GPP.(Ref: CIBET LTE-Unlicensed Josh Forgie CTS)  

Fig1: Qualcomm

                                                                       Fig2: Qualcomm

 Generally, widely deployed wireless networks fall into two main types: 1) cellular and 2) Wi-Fi. These networks have their own specific characteristics and allocated spectrum with their own licensing characteristics, simply referred to as licensed (cellular) and unlicensed (Wi-Fi). Employing LBT in the LTE-U will degrade the expectations of having a fully functional LTE-U system,  as shown in Figure 3. In fact, an LTE-U with LBT is only Wi-Fi attached to

LTE-A. Therefore, LTE-U needs to adopt a more adaptable mechanism (higher than LBT) that can be approved in countries such as the United States where regulations do not require LBT [1]. The author developed the LBT mechanism known as Adaptive LBT (ALBT), which can perform channel assessment and channel access and leave a less number of co-existence gaps in upcoming downlink operation as shown in figure 2.  

                                               Figure 2: The ALBT mechanism for LTE-U system

The author proposes spectrum etiquette that in the usage of unlicensed spectra, LTE-U should regard 802.11 WLAN as “primary user” with higher priority. Furthermore, LTE-U can access an unlicensed band only if it is detected not being used by 802.11 devices, or no harmful interference is caused to 802.11 devices [2]. The LTE-802.11 fusion protocol stack is designed at the eNB end to make LTE-U and 802.11 WLAN identify the control information of each other, based on which LTE-U adjusts its transmission model to the condition of unlicensed spectra.

In December 2013, Qualcomm released a white paper [3] describing how the recent LTE Advanced (LTE-A) updates that added the concept of carrier aggregation (CA) to LTE could be used to extend LTE-A into the unlicensed spectrum. In addition to this supplemental Downlink (SDL) mode, they also describe how TDD mode could be used to provide both downlink and uplink bandwidth just like a licensed TD-LTE network band. The white paper shows how that same spectrum could be used more efficiently with an LTE network to provide their customers with a better user experience, giving both better coverage and increased capacity over Wi-Fi deployments. The LTE-U forum (www.lteuforum.org) has concentrated on specifications for supplemental downlink (SDL) carrier aggregation scenarios. To that end, they’ve produced a number of coexistence specifications, as well as minimum requirements and conformance test specifications for both UEs and eNodeBs for SDL communication [4]-[5]. Of principal interest, however, is their technical report [6], which documents a coexistence study for LTE-U SDL from February 2015.

On the subject of standards development, in June 2015, 3GPP initiated a work item on Licensed-Assisted Access to Unlicensed Spectrum to “specify LTE enhancements for a single global solution framework for licensed-assisted access to unlicensed spectrum which enables operation of LTE in the 5GHz unlicensed spectrum for low power secondary cells
based on regional regulatory power limits using carrier aggregation [7]. Support for Dual Connectivity and standalone operation on unlicensed spectrum is therefore not included.
The LAA design should allow fair coexistence between Wi-Fi and LAA and fair coexistence between different LAA systems.” Existing solutions include heterogeneous networks and small cell deployments; in addition, operators are considering the extension of the LTE operation into the unlicensed bands. This is referred to as “LTE-Unlicensed” (LTE-U), and recently the Third Generation Partnership Project (3GPP) introduced the work item of “Licensed-Assisted Access” (LAA) to the unlicensed spectrum, where the unlicensed bands are aggregated (assisted) with the licensed bands [8].

Advances in technologies to improve spectral efficiency to improve spectral efficiency (e.g. LTE-Advanced), densifying the network through deployments of additional Wi-Fi access points and licensed-band small cells and spectrum sharing innovations [9] these all will help, but these solutions take time to develop and to deploy. In attempting to provide more immediate mobile data capacity relief, the concept of Licensed Assisted Access for LTE (LAA-LTE) has been introduced in 3GPP [10]. LAA-LTE is based on the method if carrier aggregation, where at least one of the component carriers is a licensed band carrier which supports the high QoS controls signalling. It can be challenging to define, quantifying and/or measure fairness, it is clearly stated in the study item description in 3GPP for LTE-LAA that “LAA should not impact Wi-Fi services (data, video and voice services) more than an additional Wi-Fi network on the same carrier”[11]. The two tables below show the parameters for evaluation of LAA impact on Wi-Fi without LBT and with LBT.[12]

Table 1: Parameters for evaluation of LAA impact on Wi-Fi without LBT

Table 2: Parameters for evaluation of LAA impact on Wi-Fi with LBT 

Reference:

1.      Al-Dulaimi, Anwer, et al. "5G communications race: Pursuit of more capacity triggers LTE in unlicensed band." IEEE Vehicular Technology Magazine 10.1 (2015): 43-51.

2.      Song, Hao, and Xuming Fang. "A spectrum etiquette protocol and interference coordination for LTE in unlicensed bands (LTE-U)." 2015 IEEE International Conference on Communication Workshop (ICCW). IEEE, 2015.

3.      “Extending LTE Advanced to unlicensed spectrum,” Qualcomm Incorporated, December 2013.

4.      “LTE-U SDL Coexistence Specifications,” Version 1.2, LTE-U Forum, June 2015.

5.      “eNB Conformance Test Specifications for LTE-U SDL (Modifications to 3GPP TS 36.141),” Version 1.0, LTE-U Forum, June 2015.

6.      “LTE-U Technical Report, Coexistence Study for LTE-U SDL,” Version 1.0, LTE-U Forum, February 2015.

7.      Foegelle, Michael D. "Coexistence of LTE-U and LAA in a Wi-Fi world." 2016 10th European Conference on Antennas and Propagation (EuCAP). IEEE, 2016.

8.      3GPP TR 36.889 “Study on Licensed-Assisted Access to Unlicensed Spectrum”, (Release 12) TR 36.889v1.0.1 (2015-06), 3rd Generation Partnership Project, 2015.

9.      4G Americas, “spectrum sharing ” October 2014.

10.  RWS-140029 “Chairman Summary”, 3GPP workshop on LTE in Unlicensed Spectrum, Dino Flore, June 2014.

11.  Rp-141817 “Study on licences assisted access to Unlicensed spectrum”, Ericsson, Qualcomm, Huawei, Alcatel-Lucent, December 2014.

12.  Kwan, R., et al. "Fair co-existence of licensed assisted access lte (laa-lte) and wi-fi in unlicensed spectrum." Computer Science and Electronic Engineering Conference (CEEC), 2015 7th. IEEE, 2015.