3G smartphones. ericsson White paper Uen February 2015

Transcription

1 ericsson White paper Uen February G smartphones optimizing user experience and network efficiency Rapid global smartphone uptake is creating new mobile data traffic patterns. There is an opportunity for WCDMA/HSPA network operators and device vendors to provide a better fit between changing smartphone data needs and available network capacity and capabilities. Introducing the WCDMA/HSPA features Continuous Packet Connectivity (CPC) and enhanced Forward Access Channel (efach) enables significant gains to be made both in terms of smartphone user experience and overall network efficiency.

2 Introduction The global adoption of smartphones is accelerating rapidly, and the way people use these devices in mobile networks is changing too. Voice no longer dominates: today s smartphone users are most interested in internet browsing, social media, instant messaging and mobile app usage. This is having a profound effect on the nature of traffic being carried by WCDMA/ HSPA networks the dominant technology for mobile broadband today and well into the future and how this traffic should be handled in order to deliver the best smartphone user experience in the most efficient way. Originally envisaged as a more spectrum-efficient way of serving the explosion in mobile usage (mainly for voice) almost two decades ago, WCDMA has been continuously adapted to the changing needs and expectations of mobile users. With the rise of the smartphone, the pace of development in WCDMA has accelerated, and today we see WCDMA/HSPA networks that are capable of delivering 42Mbps to mobile broadband device users far beyond the capabilities originally envisaged by WCDMA s designers. This evolution is continuing, and in 2015 will enable up to 63Mbps in the downlink and 11Mbps in the uplink in existing installed infrastructure. The challenge of maintaining smartphone user experience is a pressing one for WCDMA/ HSPA operators. The availability of mass-market, mobile broadband-capable smartphones, with prices starting at less than USD 100, is driving massive growth in smartphone subscriptions, which are estimated to rise from 2.7 billion at the end of 2014 to 6.1 billion by In the third quarter of 2014, smartphones represented between 65 to 70 percent of all mobile phones sold, compared with around 55 percent in the same quarter of 2013 [1]. Driven by the adoption of smartphones, mobile data traffic grew by 60 percent between the third quarter of 2013 and the same quarter of Mobile data traffic is expected to continue growing at a compound annual growth rate of around 40 percent over the next five years, resulting in an eightfold increase in mobile data volumes between 2014 and 2020 [2]. 3G smartphones introduction 2

3 Changing usage patterns Smartphone users are not only exploiting the growing capabilities of mobile broadband, they are also using their devices to access services that were simply not around 10 years ago. With the rise of mobile apps, social media and instant messaging, mobile data traffic is more bursty and chatty than ever before and it s always on. In between voice calls (and increasingly, real-time video sessions), today s smartphone users might send and receive many tens of thousands of small datagrams a day, which requires a continuous high-speed connection. As user behavior changes, so do traffic volume patterns. Smartphone applications have widely varying demands in terms of the timing and quantity of data they transmit. While some apps transmit large amounts of data continuously for substantial periods of time, most apps transmit small packets at intervals that might vary from fractions of a second to a matter of minutes, or longer. With smartphone data, the rapid handling of individual user requests, for instance enabled by high instantaneous data rates, improves overall network performance because controlchannel overhead is reduced and capacity for other traffic becomes available sooner. If the network and device can work together to fulfill data requests quickly and efficiently, all users will experience the benefits of reduced latency and faster round-trip times. Web browsing on a smartphone is a classic example of a bursty application, both for uplink and downlink communication. When a smartphone requests the components of a web page from the network (in the uplink), they are transferred in bursts (in the downlink), and the device acknowledges receipt of the content (in the uplink). As a result, uplink and downlink performance become tightly connected: improved uplink performance has a positive impact on downlink data rates, as well as overall system throughput. Typically, for web browsing, the downlink speed needs to be higher than the uplink speed. However, there are a growing number of services that require equal, or higher, uplink speeds including video calling and cloud synchronization. This means that continuing to develop faster data rates in both the uplink and downlink is key to improving the overall smartphone user experience. The maximum permissible uplink interference level in a cell, also known as maximum rise-over-thermal (RoT), is a key factor in WCDMA/HSPA networks. It has a direct impact on the peak data rates that the cell can deliver, as it dictates the ability of the transmitting user device to be heard clearly at the receiving radio base station. Typically, macro cells are dimensioned with an average RoT of around 7dB, which enables uplink data rates of 5.7Mbps (supported by most commercial smartphones) and secures voice and data coverage for cell-edge users. Higher data rates, such as 11Mbps and 34Mbps, require RoT levels greater than 10dB and 20dB, respectively. While there is a constant need for higher baseline capacity in mobile networks, the changing nature of mobile data means there is also an opportunity for network and device vendors to evolve the way WCDMA/HSPA networks and smartphones interact with each other to make better use of the available resources. They can provide a better fit between smartphone data needs and the available network capacity and capabilities in a way that not only boosts the efficiency of the network by delivering more usable data capacity but also enhances the user experience by delivering zippier, more consistent mobile data performance and extending smartphone battery life. Two key WCDMA/HSPA features that contribute to this enhanced experience are Continuous Packet Connectivity (CPC) and enhanced Forward Access Channel (efach). 3G smartphones Changing usage patterns 3

4 CPC minding the gaps In the fully connected HSPA High-Speed Downlink Shared Channel state, smartphone users enjoy high-speed connectivity and instantaneous response but there is a trade-off. In this connected state, the Dedicated Physical Control Channel is transmitted continuously, which drains device battery power and generates interference in the uplink. In the downlink the UE needs to monitor Downlink Shared Channel continuously. The CPC feature addresses both issues by enabling user equipment (UE) to send the control channel discontinuously meaning it can shut down its transmitter and receiver to save battery power and reduce interference (DTX) and by allowing the UE to stop monitoring Downlink Shared Channel periodically. As a result, the UE can turn off its receiver to save battery consumption (DRX). This is ideal for the kinds of chatty apps that need only intermittent connections to send relatively small datagrams. When the smartphone user does need a full HSPA connection (for example, for video calling), moving from CPC is quick and requires minimal signaling. In HSPA, each user has to overcome the interference generated from all the other users at the receiver of radio base station. Hence, with CPC, a user not only reduces its own transmit power by gating off the control channel transmission periodically, but also helps other users to further reduce their transmit power as it reduces the interference to the other users. Therefore benefits of CPC grow in line with the number of devices that have the feature enabled, and there is a systematic effect: the more UEs that use CPC, the lower the interference and the more capacity that is freed (especially in the uplink). Enabling this feature in every network and smartphone from high-end to lowest tier devices will help provide a good user experience across the board, both in terms of battery lifetime and application snappiness. 3G smartphones CPC minding the GAPS 4

5 efach higher speed on tap Measurements in live networks have shown that smartphone traffic is dominated by small datagrams. More than 50 percent of the downlink data samples are smaller than 512 bytes. This is motivation enough to improve the HSPA intermediate state, or CELL_Forward Access Channel (CELL_FACH) state. Smartphone users want to be able to rapidly access the network from a state of inactivity. This is a key reason for the introduction of the Universal Terrestrial Radio Access Network (UTRAN) Registration Area Paging Channel (URA_PCH) state, in which the device is connected but consumes very little power. Connection to the network from this state is much faster than from the idle state. If the device needs to send or receive any data, the device gets up-switched to the CELL_FACH state. This intermediate state can be reached in around 200ms, but has traditionally provided only limited throughput. Enhancements to the Forward Access Channel (FACH) states, known as High Speed Forward Access Channel (HS_FACH) for the downlink and Enhanced Uplink Forward Access Channel (EUL_FACH) for the uplink sometimes known collectively as efach improve the throughput of the intermediate states by offering higher data rates. The efach functionality can process data faster, and is therefore able to capture more traffic in the intermediate state. Furthermore, radio resource procedures can also use efach, which results in quicker channel switching and reconfigurations. On top of that, a CPC-like functionality can also be introduced for the efach state, which enables battery consumption to be reduced significantly. By offering faster connection setup and delivery of small and medium-sized data packets without the need to move to a fully connected, dedicated HSPA state this intermediate efach state improves smartphone user experience, especially for applications that do not need to send large amounts of data. By handling a greater proportion of the traffic load (especially for bursty or chatty applications), efach also frees up signaling and data transmission resources, which improves overall network performance (see Figure 1). DL FACH UL RACH Division of capacity DL HS FACH UL EUL_FACH/HS_RACH Intermediate state (semi-connected) Connected state (ordered but resource-consuming) Figure 1: efach states can take more of the data traffic load away from the fully connected HSPA state. 3G smartphones efach higher speed on tap 5

6 Live tests prove the benefits In order to optimize and align the benefits of CPC and efach features, Ericsson and Qualcomm have conducted tests both in lab and in live networks. One set of tests compared two different devices side-by-side in a WCDMA/HSPA network: one with no CPC or efach enabled, and the other with CPC and efach (HS_FACH and EUL_FACH) enabled. Both devices accessed the same antennas and were configured with receiver diversity. The applications tested included: > > a 2KB was sent every 30 seconds. > > Instant messaging modeled using a 500B ping every 30 seconds. > > Audio streaming using a radio station app. > > Video streaming playing a YouTube video. > > Web browsing downloading the same page every 60 seconds (with caching disabled). The results were largely in line with expectations, but some new insights surfaced during the tests. For example, the gains resulting from CPC/eFACH in video streaming were greater than expected: there were sufficient data activity gaps to be exploited by the UE modem, thanks to CPC, to provide an 8 percent reduction in device battery consumption during video streaming. Figure 2 shows the device-level gains achieved through CPC/ efach in the comparison tests for various applications, and significant improvements were recorded across all applications. Overall, these gains translate into improved user experience and a reduction in total smartphone power consumption of up to 25 percent. The tests also proved that the reductions in uplink interference provided by CPC and efach increase with the number of enabled devices. As more devices are equipped with these features, total uplink interference is reduced across the Application Near cell center (Tx. Pwr ~ 20dBm) Near cell edge (Tx. Pwr ~13dBm) 12.0% 18.0% IM 24.0% 25.0% Audio streaming 4.9% 19.0% Video streaming 6.9% 8.0% Web browsing 7.6% 12.3% Figure 2: Device-level power (battery) consumption savings achieved in field tests of CPC and efach for various applications. RoT gain from CPC (%) Number of UEs Figure 3: Effect on RoT gain as larger numbers of UEs are equipped with CPC. Time (seconds) % faster call setup Figure 4: Average circuit-switched (CS) call setup time for efach capable device (left) and legacy device without efach capability (right). Both devices start in URA_PCH G smartphones Live tests prove the benefits 6

7 WCDMA/HSPA network. Figure 3 shows the effect on RoT when CPC is enabled in increasing numbers of devices (UEs). The reduction in interference as CPC is enabled in each device produces shared RoT gains (which has a direct impact on the overall peak data rate available). A third positive effect on user experience is a reduction in CS call setup latency as a result of the use of signaling channels for reconfiguration, or of carrying channel switching on efach. The effect of these features on CS call setup time in a live network in Europe is illustrated in Figure 4. Another benefit is illustrated in Figure 5. Measurements are done by Ericsson on live networks showing a significant signaling (RRC messages) reduction of up to 50 percent when HS/EUL FACH is enabled, since the background traffic of popular applications can be captured by the empowered HS/EUL FACH state. This will reduce the load in the network and improves the user experience. Number of RRC messages HS/EUL FACH Enabled HS/EUL FACH Disabled Figure 5: Passive legacy device (right) and efach capable device (left) logged on to Facebook and Twitter apps left untouched for one hour. 3G smartphones Live tests prove the benefits 7

8 Conclusion These results show there are significant gains to be made both in terms of smartphone user experience and in overall network efficiency from implementing the 3GPP CPC and efach features. Operators should not only ensure these features are enabled in their WCDMA/HSPA networks, but encourage take-up of devices with these features enabled in order to meet the expectations of the fast-growing numbers of smartphone users. This white paper has been developed in collaboration with Qualcomm, Inc. 3G smartphones conclusion 8

9 GLOSSARY CELL_FACH cpc cs efach EUL_FACH FACH HS_FACH RACH Rot rrc ue URA_PCH utran CELL_Forward Access Channel Continuous Packet Connectivity circuit-switched enhanced Forward Access Channel Enhanced Uplink Forward Access Channel Forward Access Channel High Speed Forward Access Channel Reverse Access Channel rise-over-thermal Radio Resource Control user equipment UTRAN Registration Area Paging Channel Universal Terrestrial Radio Access Network 3G smartphones glossary 9

10 References 1. Ericsson, November 2014, Ericsson Mobility Report, available at: 2. Ericsson, Ericsson Mobility Report, ibid Ericsson AB All rights reserved 3G smartphones references 10