• May 13, 2011

Comprehensive Embedded Security in Microwave (Wireless) Networks

The current and ongoing migration toward IP networking on backhaul networks supports rising data volumes, which is increasing the opportunities and motivations for data and call interception. As data volumes rise in wireless networks and their associated microwave backhaul, security has become of greater concern.

This white paper presents a look at security issues, and the broad portfolio of solutions for remediating such concerns for microwave operators.

  • May 4, 2011

The World’s Longest All-IP Microwave Link

Successfully Implementing a 193-km Microwave Link over Water to Deliver 99.9995 Percent Availability

Introduction

For most designers of microwave transmission paths, engineering a reliable link over water can be a daunting task. Reflections off the water surface can play havoc with the received signal, leading to high levels of interference resulting in fading and ultimately a high level of errors and signal interruptions. For these types of paths, performance calculations using commercially available software planning tools will be insufficient to ensure superior path performance. In these cases, experience and understanding of the key parameters that influence microwave performance are critical.

Recently, Aviat Networks and our agent, Telecomunicaciones y Sistemas S.A. (TELSSA), deployed an Eclipse microwave link for Central American Corporation for Air Navigation Services (COCESNA) in Honduras that crosses over 193 km, most of which is over water. With careful design and installation, this link is now operating successfully.

COCESNA is responsible for the air traffic control over Central America territory and oceanic areas, therefore, availability of service is a critical issue.

  • April 29, 2011

Synchronization Over Microwave Mobile Backhaul Networks


Synchronization is creating quite a stir in the mobile backhaul industry as operators are wrestling with a variety of synchronization technology options including Synchronous Ethernet (SyncE) and Precision Time Protocol (PTP) a.k.a. IEEE 1588v2. This paper reviews unique microwave backhaul characteristics that need to be taken into account in support of synchronization, and how each particular synch approach can be addressed.

  • April 20, 2011

Unlocking Capacity Block Through Higher Order Digital Modulation

If you are reading this post, then you probably have heard about “4G”, the 4th generation cellular network. For a cell phone user, 4G means improved data speeds that allow faster delivery of multimedia-based applications, see our previous post, What is 4G?, for more details. On the other hand, the network operator desires to spend a minimum on upgrading network infrastructure and prefers to buy a backhaul solution that supports current and near future capacity demands of a cellular network.

Thus, it is important to improve the capacity of wireless backhaul links. To increase transmission capacity, wider channel spacing can be used. However the wireless spectrum is expensive and may not be available in some countries. Using transmission in high frequency bands, such as 60 GHz and above, provides the bandwidth needed to increase capacity. However, very high radio frequencies increase the cost of radio components. In addition, 60 GHz links limit transmission range due to high absorption of radio waves by the atmosphere, making this solution somewhat cost inefficient. One efficient way of improving the capacity of a communication link is to increase the order of the digital communication modulation scheme used for transmission.

In simple terms, digital modulation is the process of mapping a group of data bits into an information symbol that gets transmitted, after up-conversion to the radio frequency (RF) of the link. The most popular digital modulation scheme used in wireless radios is known as quadrature amplitude modulation (QAM). For a given symbol rate, increasing the modulation order, or equivalently packing more bits per symbol, would be an effective way to increase the capacity of a microwave link. For example, each symbol in a 64-QAM signal represents 6 data bits, while for 256-QAM and 1024-QAM signals it represents 8 and 10 data bits, respectively. Therefore, 1024-QAM provides (theoretically) a 25 percent increase in capacity over 256-QAM and an impressive 67 percent increase in capacity compared to 64-QAM.

The price paid for achieving such an increase in capacity is more complex signal processing algorithms and stricter requirements for channel quality, e.g. higher signal-to-noise ratio (SNR) at the receiver is required. In that case, increasing the modulation order for some networks under normal operating conditions can have a diminishing return on throughput. This is due to the fact that the required SNR for an acceptable receiver performance rarely can be met.

Why this is the case? Let us briefly discuss the challenges in increasing the modulation order. Higher modulation order results in larger pool of symbols available for transmission. For example, for 64-QAM, there exists 64 symbols in a 2D grid (known as constellation points) compared to 1,024 symbols for 1024-QAM for the same grid size. Clearly, increasing the number of symbols (assuming fixed power) makes the symbols closer to each other in this 2D grid. Thus, data detection at the receiver becomes more susceptible to errors due to impairment.

In practical terms, receiver circuits are affected by thermal noise, clipping and non-linearity of power amplifiers, phase noise and many other distortions that are beyond the scope of this post. It is worth mentioning that increasing the signal power beyond some limits results in actually decreasing the received SNR since many of these distortions associated with RF circuits are dependent on the transmitted power. Rather, the way to increase the modulation order is to improve the detection schemes and build circuits that are less susceptible to power-related distortions, along with improving the correction mechanisms at the receiver for phase noise and other impairments.

At Aviat Networks, we have the expertise and knowledge to build the highest quality microwave radios that can work at cutting edge signaling schemes. We will make sure that our customers see a sizable return—not a diminishing one from increasing the modulation order. Our pledge is that microwave backhaul will always exceed the capacity requirements of our customers.

Ramy Abdallah,

Senior Signal Processing Engineer, Aviat Networks

  • April 15, 2011

White Paper-Deploying IEEE 1588v2 Synchronization over Packet Microwave Networks

Joint Application Note with Symmetricom and Aviat Networks.

Mobile Backhaul Networks are evolving to packet, driven by 4G evolution, requiring high data and video traffic and growing number of apps, users, smartphones and tablet devices. 1588v2 microwave are a perfect match for Mobile Backhaul evolution. Paper covers 1588v2 overview, unique considerations for microwave and typical deployment scenarios (multi-hop, ring).

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