As broadcasters strive for more and more unique content, live events are growing in popularity. Consequently, productions are increasing in complexity resulting in an ever-expanding number of production staff all needing access to high quality communications. Wireless intercom systems are essential and provide the flexibility needed to host today’s highly coordinated events. But this ever-increasing demand is placing unprecedented pressure on the existing lower frequency solutions.
The 5GHz spectrum offers new opportunities as the higher carrier frequencies involved deliver more bandwidth for increased data transmission. In excess of twenty- five non-overlapping channels, each with a bandwidth of typically 20MHz, demonstrates the opportunity this technology has to outperform legacy systems based on lower frequencies such as DECT in the highly congested 2.4GHz frequency spectrum.
Although 5GHz shares the RF spectrum with Wi-Fi, use of 5GHz is not limited to Wi-Fi, and vendors dedicated to streaming reliable audio over the airwaves instead focus on optimizing transmission for audio. Specifically, this means keeping latency low and maintaining accurate audio delivery. Audio streaming intercom solutions are based on a specific 5GHz use-case to maintain high quality audio, as opposed to Wi-Fi which provides for the generalized data delivery solution and with it potentially increased latency and dropout.
RF technologies such as OFDM (Orthogonal Frequency Division Multiplexing) further improve the robustness of transmission. Rather than transmitting on one frequency, lower symbol rate audio data is spread across multiple carriers to help protect against multi-path interference and reflections, essential for moving wireless handsets or highly dynamic environments.
As 5GHz appears in the SHF range, it displays some interesting beneficial characteristics associated with this band, specifically directionality. This allows engineers to direct narrow beams and steer them to make better use of the available power. Furthermore, interference with nearby transmissions on the same frequency is reduced allowing frequency reuse.
The concept of constructive interference provides signal amplification for certain relative signal phases through constructive interference. The superimposition effect can be used to make the best use of the available transmitter power to deliver the optimal signal.
Understanding the intricacies of concepts such as short-range devices, dynamic frequency selection, and transmitter power control are key to designing the best RF intercom delivery system possible, especially when working internationally.
All this combines to make 5GHz the ideal band for reliable high-quality intercom. The directional capabilities provide greater control when planning RF coverage and blind spots can be filled using specific directional antennas.
Broadcasters rely on clear and reliable communications now more than ever, especially when we consider how many multimillion-dollar live sports events that are broadcast annually. Our reliance on intercom continues to increase and the 5GHz band provides new opportunities to further improve live broadcast production.
Radio frequency licensing authorities throughout the world have been applying pressure on broadcasters and their related services to reduce their RF spectrum allocation to allow cellular phone operators to continue to expand their coverage and provide improved services. Intercom plays a critical role in broadcasting, especially for live productions using RF mobile intercom systems, and their reliability and quality are critical.
Within the confines of a studio, production staff who tend not to be too mobile are able to work within the confines of a wired beltpack and desk mounted intercom panels. However, even with Power over Ethernet (PoE) systems, the cumbersome restrictions of trailing cables often prove to be prohibitive. To overcome this, intercom vendors started to use RF solutions within the 1.9GHz and 2.4GHz spectrums.
Vendors using the 1.9GHz and 2.4GHz also had to compete with users of Digital Enhanced Cordless Telecommunications (DECT) phones, and other devices such as mobile telephones, 2.4GHz lighting controllers, access points, Bluetooth, cordless phones, and Wi-Fi routers.
Early adopters of these frequencies were able to use them without much interference, but as the use of other devices increases, the airwaves can become clogged.
The 2.4GHz spectrum falls under the international unlicensed ISM (Industrial, Scientific, and Medical) band. The ITU (International Telecommunication Union) defined the use of this spectrum back in 1947, a long time before Wi-Fi and other users were ever considered. Although there is some variance between countries, generally, a bandwidth of 100MHz is allocated to this band providing only three or four 20MHz non- overlapping channels to be allocated (assuming a 5MHz guard band).
With all this congestion, vendors looked to the 5GHz spectrum for more space. The frequency spectrum for 5GHzunder ISM regulations does vary around the world and some of the channels available fall outside of this specification, however, up to 25 channels are available, compared to three or four in the 2.4GHz spectrum.
Each channel has 20MHz bandwidth with a 5MHz guard-band. Multiple channels can be bonded together to make combined bandwidths of 40MHz and even 80MHz. The 5GHz spectrum is divided into four distinct bands; A-Lower (5,150 to 5,250GHz), A-Upper (5,250 – 5,350GHz), B (5,470 – 5,725GHz), and C (5,735 – 5,850 GHz) with restrictions for their power and location (see figure 1).
Figure 1 – Channel allocation of 5GHz bandwidth showing maximum power and location available and how they vary for Europe, North America, and Japan. SRD, DFS and TPC are described in the text below.
Some of the frequencies are shared with the military and other mostly weather radar services. To reduce the possibility of interference from these, DFS (Dynamic Frequency Selection) is mandated in many countries. This is a “listen then transmit” function, that is, the transmitter must first listen to the channel it wants to use to confirm it cannot detect any other traffic, and only then transmit. If other users are occupying the frequency, then the transmitter must switch to one of the other channels and repeat the procedure. If none of the frequencies are available, then it simply cannot transmit. Other non-radar devices, such as Wi-Fi access points, will not prevent usage of the channels, only specific radar patterns will, and radar is unlikely to be present in most deployments.
The SRD (Short Range Device) is a unit that may just transmit, or transmit and receive, but has a low risk of interference with other devices. This is because their power output is relatively low, or they can only work in restricted areas.
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