A group of WiFi proponents will this week use a workshop convened by the 3GPP to tell the organisation that it needs to expand and formalise industry collaboration on Licensed Assisted Access (LAA). 3GPP will also be told that the WiFi experts consider there is still more to do to define LAA’s co-existence mechanisms with WiFi. The parties will insist on the primacy of 802.11-like access mechanisms, and open and neutral testing platform, as well as more simulations of different sharing scenarios.
On Saturday in Beijing, 3GPP is holding a workshop on LAA designed to allow interested parties to exchange views and information on LAA. For its part 3GPP RAN will discuss the results of its LAA feasibility study, with particular focus on coexistence analysis. The 3GPP has said that “Interested parties are warmly invited to join the discussion.” Several of them have taken up 3GPP’s invitation and have submitted their presentations.
The IEEE’s 53-page powerpoint submission insists that only 802.11-like access mechanisms will garner “evidence-based” cross-industry consensus to ensure sharing between LAA and LTE. It also alleges that 3GPP does not have processes in place to promote effective collaboration within the industry. Without that being addressed, it raises the spectre of regulatory intervention to determine sharing mechanisms.
The slide deck begins with the following statement: “The key to sharing unlicensed spectrum between LAA & 802.11 is collaboration between 3GPP & IEEE 802″. (To back that up the deck includes a dictionary definition of what collaboration means – presumably in case anyone at 3GPP in in any doubt)
IEEE is focussing on three topics for discussion in Beijing.
The first −3GPP should consider “802.11-like” access for LAA, using a collaborative development process – focusses on coexistence, which is the focus of the Beijing working group discussion and the development process.
The next two raise issues for the future:
−Has the feasibility of the macro cell scenarios in 3GPP TR 36.889 been established?
−A neutral test platform could provide a basis for collaboration between LAA & 802.11 stakeholders
The deck points out the great success of Wi-Fi, and points up its economic impact. Much of that success has been due to its “anyone, anytime, anyplace” access. That must not be put at risk. Accordingly, “an evidence-based approach suggests the use of an 80.11-like access mechanism will promote fair sharing between LAA and Wi-Fi”. It requests that “3GPP develop collaborative processes for all stakeholders to have a voice in LAA coexistence mechanisms.”
That type of access is based on Listen Before Talk (LBT) with truncated exponential back off. Other types of access will not make it. “There is unlikely to be consensus on any evidence for a new access mechanism in the planned LAA & ETSI BRAN timescales”
IEEE points out that 3GPP’s own evidence suggests 802.11-like access is suitable for sharing 5GHz channels and that 3GPP TR 36.889 recommends a Category 4 LBT mechanism, with many similarities to 802.11, for downlink (DL) data.
However, the IEEE is “concerned that 3GPP does not have processes that promote effective collaboration and thus industry consensus.” It adds that if there is not industry consensus on what constitutes “fair” access then regulators may step in – and it describes this as a “real possibility”.
It says that despite IEEE being advised that the best way to influence 3GPP is to participate directly in 3GPP, many of its participants feel their comments have been dismissed. It also doesn’t think that 3GPP’s timelines allow sufficient time for proper review by other bodies.
So, the IEEE is requesting a formal external review of LAA: IEEE 802 requests 3GPP allow formal external review for LAA, possibly based on the processes used by IEEE-SA.
Aside from these calls, the submission document makes a number of proposals, including the following:
- 3GPP to adopt an 802.1-like access mechanism for LAA.
- LAA to adopt “802.11-like” timing parameters to maximise probability of coexistence- –This approach is aligned with the Ericsson proposal in 3GPP and ETSI BRAN in relation to “defer” and “slot” times … and much of the simulation work undertaken during the 3GPP Study Item
- Define “busy” & “free” periods based on received energy & channel reservations
- divide the “free” period into slots similar to 802.11
- define a “defer period” similar to 802.11
- execute LBT and exponential back-off mechanisms before and after any transmission
- allow some control frames to be transmitted without any LBT
- count a random number of slots within a contention window as a back-off procedure
- adjust contention window based on successful & unsuccessful transmission of frames
- enable QoS using multiple “access engines” in a device (•3GPP does not appear to have considered QoS for LAA in their simulations to date)
IEEE is also querying if 3GPP has considered all questions relating to macrocell scenarios, stating that there are still “open questions relating to [two of four] macro-cell scenarios that could be subject to collaboration.”
Finally it is proposing a neutral test platform: A neutral test platform can provide fair sharing data for both the 802.11 and 3GPP communities to help inform future decisions.
The IEEE is not the only body to raise concerns. The WiFi Alliance will tell the meeting that although it is “generally pleased” with 3GPP’s direction towards a single Category 4 LBT algorithm, “significant analysis and simulation work is still required” before finalisation to ensure coexistence. Some of the required additional simulations include coexistence behaviour in multi-operator environments, in denser deployments, and with wider bandwidth Wi-Fi channels.
A submission from the Cable industry reiterates that “The development of unlicensed LTE should include input and ensure consensus from the major Wi-Fi stakeholders” – ie including cable companies. Amongst a number of proposals it wants 3GPP to clarify “basic traffic fairness definition with the fair spectrum access in terms of bandwidth and time” and also to ensure “ensure LBT cannot be switched off by removing the “framework” and configurability requirement from 3GPP specification”.
General Motors will raise issues relating to high speed access points – essentially how LAA will work when you have highly mobile WiFi APs within vehicles competing within vehicle APs , and says that viewing vehicle APs as part of existing the WiFi network results in new scenarios of high density WiFi and LAA that needs to be taken under consideration. It adds this use case to the additional simulation requirements.