a Solutions, Nokia Siemens, Samsung, and ZTE. There are also a number of Taiwanese manufac- turers that are concentrating on developing WiMAX-compatible equipment. Pre-4G Mobile Services: LTE, WiMAX, and HSPA+ The current versions of LTE, WiMAX, and HSPA+ are all pre-4G services. Mobile telephone companies are now implementing all of these services. The speeds on LTE and WiMAX can both reach ranges between 2Mbps and 25Mbps. These pre-4G ser- vices use Multiple-Input Multiple-Output (MIMO) antennas, a key factor in increased capacities. (For information on MIMO antennas, see the section "4G Multiple-Input Multiple-Output Antennas," later in this chapter.) HSPA+, also referred to as evolved HSPA, is a 3rd Generation Partnership Project (3GPP) protocol that was defined in December 2010. Like LTE and WiMAX, HSPA+ uses a MIMO antenna, which is a major improvement over HSPA. The 3GPP specified MIMO antennas for HSPA+ after it specified them for LTE and WiMAX. HSPA+ does not use Orthogonal Frequency-Division Multiplexing (OFDM) as an air interface. OFDM is capable of transmitting parallel streams simultaneously on narrow bits of spectrum. For more information on OFDM, see the section "The LTE and WiMAX Orthogonal Frequency-Division Multiplexing Air Interface," later in this chapter, as well as Figure 7-4. Although it does not use OFDM, HSPA+ does have a more efficient air interface than HSPA. To attain high speeds, HSPA+ combines carriers (bits of spectrum) from different bands to achieve high bit rates. High bit rate is synonymous with high bit rates per sec- ond. HSPA+ can also be installed using spectrum from a single carrier. The advertised speed on this is 21Mbps. However, the average attainable download speeds are 2- to 6Mbps. Mobile and Wi-Fi Networks Throughout this book, the term "carrier" has been used almost exclusively in relation to network service providers. However, as it applies to telecom- munications, the term actually has two meanings. Thus, in addition to describing a network service provider, it can