With wireless technologies moving more content to viewers, live television broadcast must adapt to consumers' lifestyles, and while an OTA connection to a fixed display device appears to have a somewhat steady audience, mobile devices are driving alternate wireless transmission schemes. The increasing demand for Internet content is making wireless networks a hot commodity for connecting devices, and some methods have already become viable for supporting wireless video. This month, we look at the details of various existing and emerging wireless video delivery methods.
One-way broadcast is evolving towards networked connections
Historically, television broadcasting has been accomplished by means of non-networked broadcasting from one source to multiple receivers. Such a scheme makes best use of the transmission spectrum when it is expected that the highest number of receivers simultaneously connect to the one broadcast. The other end of the scale, unicast, describes the situation where each receiver is ultimately connected to a unique transmitter, such as is used with cellular telephone connections or with an IP connection to a unique content source. The proliferation of content, together with an increasing demand for user personalization, is now driving a mix of the two modes towards a more networked solution. Such a network will likely combine different media and modes; hybrid broadcasting, for example, can combine broadcast from a single high-powered transmitter with unicast by means of wired and wireless LANs.
Underlying most networked systems is the concept of Media Access Control (MAC), wherein multiple terminals have access to a shared medium. These terminals can communicate with one or more servers that operate in a unicast, multicast or broadcast mode. Sharing is accomplished by time- and/or frequency-based multiplexing of information packets, with collision avoidance mechanisms. Both Ethernet and Wi-Fi operate using MAC.
Wireless networks have different characteristics that depend on the geographic coverage and can be grouped into technologies that serve customers on a physically hierarchical basis. From largest to smallest, these topologies are: WANs, wireless regional area networks (WRANs), then WLANs and wireless personal area networks (WPANs). With the increasing efficiencies of video compression, e.g., AVC/H.264 and High-Efficiency Video Coding (HEVC), it is now practical to move increasing amounts of video content over all of these networks.
Video and Internet are now key aspects of wide area and regional networks
WANs, originally designed to support cellular telephone voice traffic, use various modulation schemes based on OFDM, and include CDMA, GSM, GPRS, EDGE, EV-DO and LTE as defined by 3GPP and 3GPP2, which are collaborations between groups of telecommunications associations. (Note that the use of the well-known “3G/4G” nomenclature, while based on certain standards, is subject to some debate, resulting in imprecise definitions.) The evolutionary path of these schemes has seen increases in both QoS and data bandwidth. The basic differences between them generally concern the use of single-carrier, multicarrier or spread-spectrum modulation.
One of the newest WAN technologies is WiMAX, which is defined in the IEEE-802.16 standard. Intended for “last-mile” broadband access in the 2GHz to 66GHz spectrum, WiMAX can typically deliver 30Mb/s to 40Mb/s, with 72Mb/s (or more) possible for fixed receivers. Using a line-of-site (LOS) receive dish, WiMAX can cover an area up to about 2800sq mi (30mi radius), and thus competes readily with cable, DSL and T1 broadband services. (See Figure 1.) Non-line-of-site (NLOS) operation to mobile devices is also supported, but performance drops in both QoS and coverage area, with an expected service radius of 3mi to 10mi (314sq mi). In practice, a system can be built that combines both LOS and NLOS service, carrying LOS signals to a local base station that supports NLOS or Wi-Fi devices. WiMAX operates in both licensed and unlicensed bands, and offers multilevel encryption, making the protected distribution of paid content viable.
WRANs will soon provide broadband services in the TV bands using the new white spaces regulations of the FCC. One standard for WRANs is IEEE-802.22, which defines point-to-multipoint cognitive radio networks using fixed base stations with GPS receivers and local spectrum sensing. Centralized servers are used to maintain an active database that establishes free TV channels and guard bands to protect them. Although developed to provide for alternate uses of the TV spectrum, it's not hard to conceive of video content forming an integral part of a new broadband service.
Local networks now move considerable amounts of compressed video
WLANs are now mostly made up of Wi-Fi devices using the IEEE-802.11 family of standards. Wi-Fi devices operate in either infrastructure or ad hoc mode, at a maximum power of 100mW. In infrastructure mode, devices communicate with a central access point that, in turn, connects to a WAN or LAN. In ad hoc mode, devices connect to each other directly in a peer-to-peer arrangement. WLANs can also use bridge devices that extend the Wi-Fi coverage, which is usually limited to about 100ft. While there have been attempts to deploy citywide WLAN networks, sponsors to date have been unable to establish a viable business model using 802.11 because of the number of local nodes needed.
One of the drawbacks of 802.11 is the significant overhead needed for synchronization and data framing, resulting in the fact that the real throughput rarely comes close to the raw physical rate. For instance, 802.11g operates at a maximum physical layer bit rate of 54Mb/s but yields only about 22Mb/s average data throughput. Updates to 802.11, however, have improved both security and QoS. A newer variant, 802.11n, adds multiple-input multiple output (MIMO) operation, which uses multiple antennas and channels to increase data throughput.
At the smallest end of the scale are WPANs, which use Bluetooth, wireless USB and ZigBee technologies, typically in the 2.4GHz band. Starting with Bluetooth, which was developed as a low-cost, low-power peer-to-peer interconnect that replaces a wired connection, future WPANs are envisioned as supporting dynamic connections that a person establishes while roaming about.
Bluetooth devices come in different classes, with the most common one providing a 33ft range, using 2.5mW of power. There also exists the capability to turn on the radio only when needed for data transfer, lowering power consumption as well as aiding in security. Bluetooth low-energy technology, optimized for devices requiring maximum battery life instead of a high data transfer rate, consumes between 1/2 and 1/100 the power of classic Bluetooth technology.
ZigBee is a new WPAN technology designed for machine-to-machine applications such as smart grids, connected homes, building automation, mobile health, security and automatic control. ZigBee is a low-cost, low-power wireless mesh networking standard based on IEEE 802.15 and allows a range of over 245ft. ZigBee is designed to run for six months to two years on two AA batteries by using “time slicing,” wherein the unit operates during a transmission time slot and sleeps in between.
Multiple content pathways will become the norm
Wireless broadband has the potential to bring new services to both fixed and mobile consumers, including HD video streaming, gaming, wireless docking and displays. As these architectures are deployed, it's inevitable that video will be carried over combinations of existing and new wired and wireless distribution systems.
Aldo Cugnini is a consultant in the digital television industry and a partner in a mobile services company.
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