Aperto Networks Inc. has banked a further $20 million from its investors, the WiMax equipment specialist announced Wednesday.

The Series F round takes Aperto's total funding since its 1999 formation to a whopping $159 million; its previous funding round was announced in February 2007. (See Friday Funding Roundup.)

The new cash injection was led by Saratoga, Calif.-based Quicksilver Ventures, which was joined by a number of Aperto's existing backers, including Gunn Allen Venture Partners, JK&B Capital , Canaan Partners , Alliance Ventures , Innovacom , Jafco Ventures , and Labrador Ventures

The vendor, which also hit the CTIA newswires Tuesday with support for additional frequencies, says it's now supplying its fixed and mobile WiMax products to more than 100 carrier and enterprise customers around the world, and claims to be the only vendor to have a WiMax base station that supports and operates both fixed and mobile WiMax simultaneously. (See Aperto Adds Frequencies, OTE Picks Aperto PacketMAX, and BSNL Deploys Aperto.)

Aperto's funding news is just one of a number of WiMax announcements being made at the CTIA tradeshow in Las Vegas this week, and comes as the industry continues to debate just how fast WiMax services will catch on with subscribers. (See CTIA & the Future of 4G, CTIA: Sprint's Samsung Touch, WiMax Goes Prepaid, and CTIA Photos, Part I.)

For instance, the WiMAX Forum forecasts there will be more than 133 million people using WiMax services by 2012. (See CTIA & the Future of 4G.)

But research firm Senza Fili Consulting LLC forecasts there will be about 54 million WiMax users by 2012.

Last week research firm Maravedis Inc. reported there were just 1.7 million users of broadband wireless/WiMax services globally at the end of 2007. Maravedis estimates there will be about 110 million WiMax users by the end of 2013. (See Maravedis Reports Stats.)

— Ray Le Maistre, International News Editor, Light Reading