Indoor Wireless Communications: From Theory to Implementation provides an in-depth reference for design engineers, system planners and post graduate students interested in the vastly popular field of indoor wireless communications. It contains wireless applications and services for in-building scenarios and knowledge of key elements in the design and implementation of these systems. Technologies such as Wireless Local Area Networks, Bluetooth, ZigBee, Indoor Optical Communications, WiMAX, UMTS and GSM for indoor environments are fully explained and illustrated with examples. Antennas and propagation issues for in-building scenarios are also discussed, emphasizing models and antenna types specifically developed for indoor communications. An exhaustive survey on indoor wireless communication equipment is also presented, covering all available technologies including antennas, distribution systems, transceivers and base stations.
Dr. Alejandro Aragón-Zavala, Tecnológico de Monterrey, Campus Querétaro, México
Dr. Aragón-Zavala graduated from Tecnológico de Monterrey, Campus Querétaro as Electronics and Communications Engineer in December 1991. In 1998 he received his MSc in Satellite Communication Engineering from the University of Surrey, and in 2003 his PhD in Antennas and Propagation at the same university. He has worked as an engineer and consultant in the industry, and since 2003, Dr. Aragón-Zavala has been the Academic Director of the former IEC and ISE undergraduate programs at the Tecnológico de Monterrey, Campus Querétaro, and is in charge of ITE (all Electronic Engineering degrees). His research interests include: mobile communications, satellite systems, high-altitude platform systems, antenna design and indoor propagation.
Currently around 70% of mobile usage is inside buildings and some analysts predict that in the next few years around 90% of mobile usage will take place indoors (Paolini, 2011), be it at home, in the office or in public buildings, with the majority of that being in an individual user's home and main office locations. Traditionally such services have been provided on an 'outside-in' basis from macrocells, which were originally deployed to provide voice coverage to vehicles travelling along major roads. This conventional architecture is increasingly limited in its ability to meet modern mobile users' needs for reliable indoor mobile service because:
- The increased volume of mobile data use puts a greater load on macrocell capacity to deliver a reliable service.
- User expectations of the minimum data rate that constitutes a viable service are continuing to increase and are dominated by the indoor locations in which they mostly consume services.
- Modern mobile devices have to support a wide range of frequency bands in a small-form factor, reducing their sensitivity and hence increasing the signal strength needed to achieve a given coverage.
- Improved thermal insulation properties of buildings lead to an increase in the use of denser and more conductive external construction materials, including metallized windows, increasing the losses that radio waves encounter in penetrating a building.
- Increased use of high-frequency bands at 2.1 GHz, 2.4 GHz, 2.6 GHz, 3.5 GHz and beyond, which suffer greater losses than frequencies below 1 GHz.
- Economic incentives for mobile operators to share macrocell networks, reducing the diversity of options for users to switch to operators who do have macrocell coverage close to the locations they care most about.
In consumer surveys, mobile users frequently cite poor in-building coverage as the number one network-related reason to turn to other operators. Increased mobile data usage has changed customer priorities and expectations. Smartphone users rate the importance of messaging and Internet quality 2.5 times higher than standard phone users. Even the average phone user rated network quality as the most important reason for choosing a mobile operator. Mobile Internet is much more demanding than a few years ago, requiring Wi-Fi coverage as a 'default' commodity. All these factors increase the need of specialized indoor radio technologies to satisfy such user expectations and demands.
A recent global mobile consumer survey audit conducted by Deloitte (2012) examined the use of Wi-Fi by mobile users and found:
- In the UK, Wi-Fi is the main Internet connection for smartphones at nearly 60%.
- The desire for faster, more reliable connectivity is the principal driver of Wi-Fi usage over cellular mobile.
- Almost 90% of both smartphone and tablet users connect to the Internet using Wi-Fi from home.
Given this and the potential loss in consumer and societal benefits arising from poor in-building services, it is very relevant to consider the planning and design of in-building radio systems following a methodological and engineering approach, considering:
- The types of indoor wireless technologies and their characteristics
- Design requirements and standards for coverage and capacity
- Voice and data traffic considerations when deploying an indoor radio solution
- The physics of in-building radio propagation
- Channel modelling options that are available to estimate coverage in an indoor radio system
- Available RF and antenna equipment for indoor systems
- Measurement techniques and systems used to design and validate in-building networks
- Practical issues related to indoor radio design and deployment that could be useful for engineers, students and scientists.
1.2 Evolution of Macro to Heterogeneous Networks
The changing shape of mobile networks from the traditional macrocell approach to what is known as heterogeneous networks or 'HetNets' (a mix of macro and small-cell architectures) can both resolve issues for the operator but at the same time create potential policy problems for telecommunications regulators, notably:
- Future demand for spectrum. The indoor layer of the network starts to soak up the rapid increase in demand and the value of future mobile spectrum allocations may be reduced.
- Interference management. Current policy stipulates that coordination between multioperators should be resolved by each party. A market-driven change into the network architecture may impact the regulatory policy in this area.
- Competition between MNOs. Competition may start to be reduced by the growing use of multioperator collaborations on both the core network and on the Radio Access Network.
- Incentives for investment. There may come a time when operators reduce their level of investment in the macronetwork to focus on serving the indoor consumers with smaller more cost effective building solutions.
- Consumer switching. This is encouraged by operators marketing their new products and services.
Traditionally, when MNOs first deployed their mobile networks they were designed for:
- Wide area coverage
- Targeting mobile voice
However, in today's network topology the demand from users has dramatically shifted towards the consumption of data anywhere, anytime, which has led to the following trends:
- Usage is predominantly indoors (70-90% of the traffic by volume) (Analysis Mason Ltd, 2011).
- The indoor locations of relevance are predominantly just two per person (my home, my office), that is not just geographical coverage.
- Indoor coverage is often cited by operators as the number one network-related cause of churn.
- Smartphones have poorer sensitivity than traditional phones - and it gets worse as more bands are added.
- Even voice is increasingly on 3G and LTE: better link budget, but mainly 2.1 GHz today.
- User expectation of what constitutes the minimum acceptable data rate increases with time (as does expectation of typical rates).
- Building regulations increasingly specify thermal insulation requirements, which are increasingly being met by metallized glass, significantly increasing attenuation.
There are three broad indoor user environments to consider for in-building systems. These are in the home, in the office or in a public building/venue. There are distinct differences in terms of both achieving coverage and satisfying capacity in each of these environments that impact the scale of the market and the optimum technical solution when considering indoor solutions.
This book aims at presenting methods and techniques of how in-building coverage can be enhanced relative to that provided by the existing (predominantly macrocell-based) networks at predominantly a technical level but including also some commercial level detail. For example, one particular challenge to be addressed for anyone interested in designing an in-building radio system may be openness of any systems and we ask the question: 'What do we mean by "allowing access to different operators"?' The following points attempt to provide some possible solutions:
- One solution can simultaneously handle users with different operators.
- Solutions are cheap, unobtrusive and simple enough to permit multiples of them in one location if needed.
- It could work for any operator and can be changed between operators at the user's choice (but only phones from one operator at a time).
- It is easy and cheap to switch operators even if one 'box' cannot handle multiple operators.
- Allow consumers to take action themselves rather than 'begging' an operator; for example, three currently limit femtocells to those who they consider have a valid coverage problem.
- How does this compare and contrast with being able to move your phone between providers, move contracts between providers or move gateways/home hubs between providers.
The increased use of Wi-Fi presents further challenges and issues to cellular operators and good knowledge of the technology is mandatory for deploying a whole radio network, as nowadays Wi-Fi needs to coexist with cellular and other wireless technologies. Following this trend, mobile operators are beginning to adopt Wi-Fi as a complementary service as an in-building solution, principally to help offloading capacity constrained parts of the network. However, there are still some technical issues from Wi-Fi that, once overcome, will provide a more integrated solution for mobile operators.
The overriding issue for operators is one of cost: while macrocells have technical challenges in addressing remaining in-building demand, they have the benefit of spreading the costs over large numbers of users, resulting in the former operator mantra 'outside-in always wins'. Provision of in-building systems for every building with a need has hitherto been excessively expensive, in both equipment and professional services.
New technologies do provide opportunities to significantly reduce the cost of provision, but significant work remains to encourage widespread roll-out of these technologies, including consumer understanding, commercial incentives and regulatory clarity. Some of these...