无线频道的价值何在？

无线频道的价值何在？

Tom Sun

       香港是全球生活指数最高的城市之一。在香港，百万美元只能买到一间200平方英尺的小屋。近期，于美国举办的AWS-3频谱拍卖中，AT&T耗资182亿美元买下了覆盖全美的20MHZ的频段。同样的一百万美元，也只能租用1KHz的得到许可的频段若干年而已。为什么运营商要耗费如此巨资，来确保其拥有将电磁脉冲在空间发送的权利呢？

       先从无线频道的定义说起吧：它指的是用于广播或无线电通信的特定无线电频率的通道。在移动应用中，它提供了我们的移动设备与无线接入网之间的链接。简而言之，如果没有无线频道，就根本没有移动业务可言。

       将电磁波在空中发送与接收的方法仅仅在140年前才被发现。苏格兰科学家James Clerk Maxwell率先预测，电磁扰动可以按光速以波的特性在真空中传播。Heinrich Hertz则在其卓越的无线实验中展示了无线电波的首次发送与接收，从而证实了该项假设。

       电磁波可以按从8.3 kHz到3,000 GHz范围内的频率进行振动。打个比方来说，如果将用于Wi-Fi的40 Mhz频段比作一公里的距离，总共就需要75,000公里来覆盖整个无线频谱——这是环绕地球一圈半的长度。既然资源如此丰富，为何有人愿意花费180亿美元的巨资，单单只是为了租用20Mhz的频段？感觉确实有些荒谬。显而易见，并非所有频段的价值都是均等的。

       空气以及其他物理间隔如地域、树木以及建筑物等均限制着无线电波的传播。总起来说，对于地面传输而言，在相同有效发射功率的条件下，较低频率的无线电波比较高频率的无线电波要传播得更远。这就是为什么在偏远地区，在较低频带上运作的AM无线信号比FM无线信号要传播得更远，也更容易接收到的原因。正因为如此，对移动通信而言，低于4GHz的频段要更加合用。

       许多国际国内的标准组织均对无线频率的使用进行了规定与管制。在美国，相关的频谱管理由联邦通信委员会负责（Federal Communications Commission(FCC)）。作为“频道”流量控制的机构，FCC将不同频率分配给军事机构、广播企业以及用于无线通信。随着可供使用的频段逐步减少，而需求不断增加，自然而然，新频带的价格就水涨船高了。

       新频带的推出既为移动市场带来了机遇，也产生了一定的不确定性。移动设备供应商将其视作销售更多RAN设备的契机，但与此同时，要在已然超出100种之多的产品队伍中再增加新的无线设备品种，也令运营商头痛不已。

       PMC推出的 UniTRX™ 芯片集的一个重要价值点就在于它能支持从400MHz到4 GHz的所有频带——基本上涵盖了经过授权许可的所有可用于移动通信的频带。如此高的灵活度让移动设备供应商得以跨越多个频带而重复使用相同的RF设计。采用该芯片集的客户因而可以大幅度地缩短产品开发时间，从而能够更好地把握新频带的推出所带来的市场机遇。

 

 WHAT is the value of an airway?

        Hong Kong is one of the most expensive cities in the world to live in. Over there, one million dollars can buy you a200 square foot home. In a recent AWS-3 spectrum auction in the US, AT&Tspent $18.2 billion for a nationwide 20 MHz airway. The same one million dollars can rent you 1KHz of licensed spectrum for a few years. Why are operators spending so much money to secure the rights to send some electromagnetic pulses through the air?

        Let’s start with the definition of anairway:  it is a channel of a designated radio frequency used for broadcasting or radio communication. In mobile applications, it provides the linkage between our mobile devices and the radio access network. Simply put, if you don’t have an airway, you can’t have mobile service.

       The concept of sending and receiving electromagnetic waves over the air was discovered only 140 years ago. The Scottish scientist James Clerk Maxwell first predicted that electromagnetic disturbances should propagate through a vacuumat the speed of light in a wave-like characteristic. This hypothesis was later confirmed by Heinrich Hertz in his brilliant wireless experiments that demonstrated the first transmission and reception of radio waves.

        An electromagnetic wave can oscillate in frequencies ranging from 8.3kHz to 3,000 GHz. As an analogy, if you equate the 40 MHz band used for Wi-Fito one kilometer in distance, it would take up to 75,000 kilometers to coverthe entire radio spectrum—a distance that is one and half times around the earth. With such an abundant resource, it seems absurd for someone to spend $18billion just to rent 20 MHz of airway. Clearly, not all frequencies have equalvalue.

       The atmosphere and other physicalbarriers like terrain, trees and buildings limit the propagation of radiowaves. In general for terrestrial transmission, a lower frequency radio wave travels farther than a higher frequency radio wave given the same effective radiated power.

       Thisis why AM radio signals, which operate in lower frequency band, traverse farther and are easier to pick up than FM radio signals in remote areas. Forthis reason, lower frequency bands below 4 GHz are more desirable for mobile communication.

       The use of radio frequency is regulated by various international andnational standard bodies. In the United States, this spectrum management process is the responsibility of Federal Communications Commission (FCC). Actingas the “airway” traffic controller, the FCC assigns frequencies to military,broadcasting bodies and for mobile communication. As the demand increases with dwindling supply, the price for new frequency bands naturally goes up.

       The introduction of a new band creates bothopportunity and uncertainty for the mobile market. Mobile equipment suppliers see this as an opportunity to sell more RAN equipment, but at the same time grimace at the need to add yet another radio variant to a portfolio already overflowing with more than 100 product variants.

       One of the values of PMC’s UniTRX™ chipset is its ability to support bands from 400 MHzto 4 GHz—essentially all  of the bands licensed for mobile communication.This flexibility allows mobile equipment suppliers to reuse a common RF designacross multiple frequency bands. By helping our customers to drastically reduce their product development time, they are better positioned to capture the opportunity created by the introduction of a new band.